[plt-scheme] likely -> incompatibility: hashtables

From: Graham Hughes (graham at sigwinch.org)
Date: Mon Apr 7 19:45:59 EDT 2008

Jos Koot wrote:
> I always thought a relation was defined as a subset of the product of
> two (or even more) sets (not necessarily different ones, of course)
> Jos

They're equivalent.  A map is a function is a subset of A x B with
certain restrictions (for all a in A, there is exactly one b in B where
(a,b) is in the function; partial function is "at most one b in B").  We
can regard a relation, a subset of A x B, as a function from A onto the
power set of B such that the function returns every b in B so (a,b) is
in the relation.


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