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(Or extensionality). Functions, f and g are extensionally
equal if and only if
f x = g x for all x.
where "=" means both expressions fail to terminate (under some
given reduction strategy
) or they both terminate with the
same basic value.
Two functions may be extensionally equal but not
inter-convertible (neither is reducible to the other). E.g.
\ x . x+x and \ x . 2*x. See also observational equivalence, referential transparency.
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