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''Update functions'' in Scheme.
Date: Thu, 19 May 88 10:35:23 EDT
From: Mitchell Wand <email@example.com>
One ought not to say things like:
"F(G(C)) := D ought to ensure that F(G(C)) = D afterwards."
too blithely. Consider the array assignment:
A[A] := 2
in a two element array A, where initially A=A=1 . This sort of thing had
program verifiers confused for a good while in the early 70's.
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Now consider the array assignment Y(A[.]) := 2 . :-)