34 KiB
title | TARGET DECK | FILE TAGS | tags | |||
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Equivalence Transformation | Obsidian::STEM | programming::equiv-trans |
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Overview
Equivalence-transformation refers to a class of calculi for prop-logic derived from negation (\neg
), conjunction (\land
), disjunction (\lor
), implication (\Rightarrow
), and equality (=
).
Gries covers two in "The Science of Programming": a system of evaluation and a formal system. The system of evaluation mirrors how a computer processes instructions, at least in an abstract sense. The formal system serves as a theoretical framework for reasoning about propositions and their transformations without resorting to "lower-level" operations like substitution.
%%ANKI Basic Who is the author of "The Science of Programming"? Back: David Gries Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Cloze
Gries replaces logical operator {\Leftrightarrow
} in favor of {=
}.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What Lean theorem justifies Gries' choice of =
over \Leftrightarrow
?
Back: propext
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
Tags: lean
END%%
%%ANKI Basic What are the two calculi Gries describes equivalence-transformation with? Back: A formal system and a system of evaluation. Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
Equivalence Schemas
A proposition is said to be a tautology if it evaluates to T
in every state it is well-defined in. We say propositions E1
and E2
are equivalent if E1 = E2
is a tautology. In this case, we say E1 = E2
is an equivalence.
%%ANKI Basic What does it mean for a proposition to be a tautology? Back: That the proposition is true in every state it is well-defined in. Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
How is tautology e
written equivalently with a quantifier?
Back: For free identifiers i_1, \ldots, i_n
in e
, as \forall (i_1, \ldots, i_n), e
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI Basic The term "equivalent" refers to a comparison between what two objects? Back: Expressions. Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What does it mean for two propositions to be equivalent?
Back: Given propositions E1
and E2
, it means E1 = E2
is a tautology.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What is an equivalence?
Back: Given propositions E1
and E2
, tautology E1 = E2
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
How is \Rightarrow
written in terms of other logical operators?
Back: p \Rightarrow q
is equivalent to \neg p \lor q
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
How is \Leftrightarrow
/=
written in terms of other logical operators?
Back: p \Leftrightarrow q
is equivalent to (p \Rightarrow q) \land (q \Rightarrow p)
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI Basic What distinguishes an equality from an equivalence? Back: An equivalence is an equality that is also a tautology. Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
Equivalence Rules
- Rule of Substitution
- Let
P(r)
be a predicate andE1 = E2
be an equivalence. ThenP(E1) = P(E2)
is an equivalence.
- Let
- Rule of Transitivity
- Let
E1 = E2
andE2 = E3
be equivalences. ThenE1 = E3
is an equivalence.
- Let
%%ANKI Basic What two inference rules make up the equivalence-transformation formal system? Back: Substitution and transitivity. Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI Basic Which of the two inference rules that make up the equivalence-transformation formal system is redundant? Back: Transitivity. Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What does the rule of substitution say in the system of evaluation?
Back: Let P(r)
be a predicate and E1 = E2
be an equivalence. Then P(E1) = P(E2)
is an equivalence.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI Basic How is the rule of substitution written as an inference rule (in standard form)? Back:
\begin{matrix}
E1 = E2 \\
\hline P(E1) = P(E2)
\end{matrix}
END%%
%%ANKI
Basic
What does the rule of transitivity state in the system of evaluation?
Back: Let E1 = E2
and E2 = E3
. Then E1 = E3
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI Basic How is the rule of transitivity written as an inference rule (in standard form)? Back:
\begin{matrix}
E1 = E2, E2 = E3 \\
\hline E1 = E3
\end{matrix}
END%%
%%ANKI Cloze The system of evaluation has {equivalences} whereas the formal system has {theorems}. Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI Basic What is a "theorem" in the equivalence-transformation formal system? Back: An equivalence derived from the axioms and inference rules. Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI Basic How is e.g. the Law of Implication proven in the system of evaluation? Back: With truth tables. Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI Basic How is e.g. the Law of Implication proven in the formal system? Back: It isn't. It is an axiom. Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Cloze
The system of evaluation and formal system are connected by the following biconditional: {e
is a tautology} iff {e = T
is a theorem}.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Cloze
The {1:system of evaluation} is to {2:"e
is a tautology"} whereas the {2:formal system} is to {1:"e = T
is a theorem"}.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
Substitution
Textual substitution refers to the simultaneous replacement of a free identifier with an expression, introducing parentheses as necessary. This concept is just the #Equivalence Rules with different notation. Let \bar{x}
denote a list of distinct identifiers. If \bar{e}
is a list of expressions of the same length as \bar{x}
, then simultaneous substitution of \bar{x}
by \bar{e}
in expression E
is denoted as $E_{\bar{e}}^{\bar{x}}
$
Note that simultaneous substitution is different than sequential substitution.
%%ANKI Basic Textual substitution is derived from what equivalence rule? Back: The substitution rule. Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What term refers to x
in textual substitution E_e^x
?
Back: The reference.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What term refers to e
in textual substitution E_e^x
?
Back: The expression.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What term refers to both x
and e
together in textual substitution E_e^x
?
Back: The reference-expression pair.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What identifier is guaranteed to not occur freely in E_e^x
?
Back: N/A.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What identifier is guaranteed to not occur freely in E_{s(e)}^x
?
Back: x
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Why does x
not occur freely in E_{s(e)}^x
?
Back: Because s(e)
evaluates to a constant proposition.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What is the role of E
in textual substitution E_e^x
?
Back: It is the expression in which free occurrences of x
are replaced.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What is the role of e
in textual substitution E_e^x
?
Back: It is the expression that is evaluated and substituted into E
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What is the role of x
in textual substitution E_e^x
?
Back: It is the identifier matching free occurrences in E
that are replaced.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
How is textual substitution E_e^x
interpreted as a function?
Back: As E(e)
, where E
is a function of x
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Why does Gries prefer notation E_e^x
over e.g. E(e)
?
Back: The former indicates the identifier to replace.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What two scenarios ensure E_e^x = E
is an equivalence?
Back: x = e
or no free occurrences of x
exist in E
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
If x \neq e
, why might E_e^x = E
be an equivalence despite x
existing in E
?
Back: The only occurrences of x
in E
may be bound.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What is required for E_e^x
to be valid?
Back: Substitution must result in a syntactically valid expression.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What is the result of the following? (x < y \land (\forall i : 0 \leq i < n : b[i] < y))_z^x$$
Back:
(z < y \land (\forall i : 0 \leq i < n : b[i] < y))
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What is the result of the following? (x < y \land (\forall i : 0 \leq i < n : b[i] < y))_z^y$$
Back:
(x < z \land (\forall i : 0 \leq i < n : b[i] < z))
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What is the result of the following? (x < y \land (\forall i : 0 \leq i < n : b[i] < y))_z^i$$
Back:
(x < y \land (\forall i : 0 \leq i < n : b[i] < y))
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
In textual substitution, what does e.g. \bar{x}
denote?
Back: A list of distinct identifiers.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What is the role of E
in textual substitution E_{\bar{e}}^{\bar{x}}
?
Back: It is the expression in which free occurrences of \bar{x}
are replaced.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What is the role of \bar{e}
in textual substitution E_{\bar{e}}^{\bar{x}}
?
Back: It is the expressions that are substituted into E
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What is the role of \bar{x}
in textual substitution E_{\bar{e}}^{\bar{x}}
?
Back: It is the distinct identifiers matching free occurrences in E
that are replaced.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
Arrays
An array can be seen as a function from the domain of the array to the subscripted values found in the array. We denote array subscript assignment similarly to state identifier assignment: (b; i{:}e)[j] = \begin{cases} i = j \rightarrow e \ i \neq j \rightarrow b[j] \end{cases}
%%ANKI
Basic
Let b
be an array. What does b.lower
denote?
Back: The lower subscript bound of the array.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b
be an array. What does b.upper
denote?
Back: The upper subscript bound of the array.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b
be an array. How is domain(b)
defined in set-theoretic notation?
Back: \{i \mid b.lower \leq i \leq b.upper\}
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b[0{:}2]
be an array. What is b.lower
?
Back: 0
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b[0{:}2]
be an array. What is b.upper
?
Back: 2
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Execution of b[i] := e
of array b
in state s
yields what new value of b
?
Back: b = (b; i{:}s(e))
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let s
be a state. What is x
in (s; x{:}e)
?
Back: An identifier found in s
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let s
be a state. What is e
in (s; x{:}e)
?
Back: An expression.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let s
be a state. What is e
's type in (s; x{:}e)
?
Back: A type matching x
's declaration.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b
be an array. What is x
in (b; x{:}e)
?
Back: An expression that evaluates to a member of domain(b)
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b
be an array. What is e
's type in (b; x{:}e)
?
Back: A type matching b
's member declaration.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b
be an array. What case analysis does (b; i{:}e)[j]
evaluate to?
Back: (b; i{:}e)[j] = \begin{cases} i = j \rightarrow e \ i \neq j \rightarrow b[j] \end{cases}
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b
be an array. How is (((b; i{:}e_1); j{:}e_2); k{:}e_3)
rewritten without nesting?
Back: As (b; i{:}e_1; j{:}e_2; k{:}e_3)
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b
be an array. How is (b; (i{:}e_1; (j{:}e_2; (k{:}e_3))))
rewritten without nesting?
Back: N/A. This is invalid syntax.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b
be an array. How is (b; i{:}e_1; j{:}e_2; k{:}e_3)
rewritten with nesting?
Back: As (((b; i{:}e_1); j{:}e_2); k{:}e_3)
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b
be an array. What does (b; i{:}2; i{:}3; i{:}4)[i]
evaluate to?
Back: 4
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b
be an array. How is (b; 0{:}8; 2{:}9; 0{:}7)[1]
simplified?
Back: As b[1]
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI Basic According to Gries, what is the traditional interpretation of an array? Back: As a collection of subscripted independent variables (with a common name). Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI Basic According to Gries, what is the new interpretation of an array? Back: As a function. Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What propositional expression results from eliminating (b; \ldots)
notation from (b; i{:}5)[j] = 5
?
Back: (i = j \land 5 = 5) \lor (i \neq j \land b[j] = 5)
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What logical axiom is used when eliminating (b; \ldots)
notation from e.g. (b; i{:}5)[j] = 5
?
Back: The Law of the Excluded Middle.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Cloze
For state s
and array b
, {(s; x{:}s(x))
} is analagous to {(b; i{:}b[i])
}.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What is the simplification of (b; i{:}b[i]; j{:}b[j]; k{:}b[j])
?
Back: (b; k{:}b[j])
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Given array b
, what terminology does Gries use to describe i{:}j
in e.g. b[i{:}j]
?
Back: A section.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Given array b
, how many elements are in section b[i{:}j]
?
Back: j - i + 1
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Given array b
and fixed j
, what is the largest possible value of i
in b[i{:}j]
?
Back: j + 1
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Given array b
, how many elements are in b[j{+}1{:}j]
?
Back: 0
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Given array b
, what is b[1{:}5] = x
an abbreviation for?
Back: \forall i, 1 \leq i \leq 5 \Rightarrow b[i] = x
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Given array b
, what is b[1{:}k{-}1] < x < b[k{:}n{-}1]
an abbreviation for?
Back: (\forall i, 1 \leq i < k \Rightarrow b[i] < x) \land (\forall i, k \leq i < n \Rightarrow x < b[i])
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
Selector Update Syntax
A selector denotes a finite sequence of subscript expressions, each enclosed in brackets. \epsilon
denotes the empty selector. We can generalize the above to all variable types as follows: \begin{align*} (b; \epsilon{:}g) & = g \ (b; [i] \circ s{:}e)[j] & = \begin{cases} i \neq j \rightarrow b[j] \ i = j \rightarrow (b[j]; s{:}e) \end{cases} \end{align*}
%%ANKI Basic What is a selector? Back: A finite sequence of subscript expressions. Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Given valid expression (b; [i]{\circ}s{:}e)
, what can be said about i
?
Back: i
is in the domain of b
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What is the base case of selector update syntax?
Back: (b; \epsilon{:}g) = g
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
The null selector is usually denoted as what?
Back: \epsilon
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI Basic The null selector is the identity element of what operation? Back: Concatenation of sequences of subscripts. Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
How is assignment x := e
rewritten with a selector?
Back: x \circ \epsilon := e
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
How is x \circ \epsilon := e
rewritten using selector update syntax?
Back: x := (x; \epsilon{:}e)
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What assignment expression (i.e. using :=
) is simpler but equivalent to x := (x; \epsilon{:}e)
?
Back: x := e
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What two assignments (i.e. using :=
) are used to prove e = (x; \epsilon{:}e)
?
Back: x := e
and x \circ \epsilon := e
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
How do assignments x := e
and x \circ \epsilon := e
prove e = (x; \epsilon{:}e)
?
Back: The assignments have the same effect and the latter can be written as x := (x; \epsilon{:}e)
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b
be an array. How is b[i][j] := e
rewritten using selector update syntax?
Back: b := (b; [i][j]{:}e)
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b
be an array. What does (b; \epsilon{:}g)
evaluate to?
Back: g
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b
be an array and i = j
. What does (b; [i]{\circ}s{:}e)[j]
evaluate to?
Back: (b[j]; s{:}e)
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Let b
be an array and i \neq j
. What does (b; [i]{\circ}s{:}e)[j]
evaluate to?
Back: b[j]
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Maintaining selector update syntax, how is (c; 1{:}3)[1]
more explicitly written with a selector?
Back: (c; [1]{:}3)[1]
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Maintaining selector update syntax, how is (c; 1{:}3)[1]
rewritten with [1]
commuted as leftward as possible?
Back: (c[1]; \epsilon{:}3)
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
Theorems
(E_u^x)_v^x = E_{u_v^x}^x
- The only possible free occurrences of
x
that may appear after the first of the sequential substitutions occur inu
.
- The only possible free occurrences of
%%ANKI
Basic
How do we simplify (E_u^x)_v^x
?
Back: As E_{u_v^x}^x
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
How is E_{u_v^x}^x
rewritten as sequential substitution?
Back: As (E_u^x)_v^x
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Why is (E_u^x)_v^x = E_{u_v^x}^x
an equivalence?
Back: After the first substitution, the only possible free occurrences of x
are in u
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
- If
y
is not free inE
, then(E_u^x)_v^y = E_{u_v^y}^x
.y
may not be free inE
but substitutingx
withu
can introduce a free occurrence. It doesn't matter if we perform the substitution first or second though.
%%ANKI
Basic
In what two scenarios is (E_u^x)_v^y = E_{u_v^y}^x
always an equivalence?
Back: x = y
or y
is not free in E
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
If x \neq y
, when is (E_u^x)_v^y = E_{u_v^y}^x
?
Back: When y
is not free in E
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Why should y
not be free in E
for (E_u^x)_v^y = E_{u_v^y}^x
to be an equivalence?
Back: If it were, a v
would exist in the LHS that doesn't in the RHS.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
How does Gries denote state s
with identifer x
set to value v
?
Back: (s; x{:}v)
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
How is (s; x{:}v)
written instead using set-theoretical notation?
Back: (s - \{\langle x, s(x) \rangle\}) \cup \{\langle x, v \rangle\}
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Execution of x := e
in state s
terminates in what new state?
Back: (s; x{:}s(e))
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Given state s
, what statement does (s; x{:}s(e))
derive from?
Back: x := e
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
What missing value guarantees state s
satisfies equivalence s = (s; x{:}\_)
?
Back: s(x)
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Given state s
, why is it that s = (s; x{:}s(x))
?
Back: Evaluating x
in state s
yields s(x)
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
s(E_e^x) = s(E_{s(e)}^x)
- Substituting
x
withe
and then evaluating is the same as substitutingx
with the evaluation ofe
.
- Substituting
%%ANKI
Basic
How can we simplify s(E_{s(e)}^x)
?
Back: As s(E_e^x)
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Given state s
, what equivalence relates E_e^x
with E_{s(e)}^x
?
Back: s(E_e^x) = s(E_{s(e)}^x)
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
- Let
s
be a state ands' = (s; x{:}s(e))
. Thens'(E) = s(E_e^x)
.
%%ANKI
Cloze
Let s
be a state and s' = (
{s; x{:}s(e)
})
. Then s'(
{E
}) = s(
{E_e^x
})
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
If s' = (s; x{:}s(e))
, then s'(E) = s(E_e^x)
. Why do we not say s' = (s; x{:}e)
instead?
Back: The value of a state's identifier must always be a constant proposition.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
How do you define s'
such that s(E_e^x) = s'(E)
?
Back: s' = (s; x{:}s(e))
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
%%ANKI
Basic
Given defined value v \neq s(x)
, when is s(E) = (s; x{:}v)(E)
?
Back: When x
is not free in E
.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
- Given identifiers
\bar{x}
and fresh identifiers\bar{u}
,(E_{\bar{u}}^{\bar{x}})_{\bar{x}}^{\bar{u}} = E
.
%%ANKI
Basic
When is (E_{\bar{u}}^{\bar{x}})_{\bar{x}}^{\bar{u}} = E
guaranteed to be an equivalence?
Back: When \bar{x}
and \bar{u}
are all distinct identifiers.
Reference: Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
END%%
Bibliography
- Avigad, Jeremy. ‘Theorem Proving in Lean’, n.d.
- Gries, David. The Science of Programming. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.