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\DOC mem'
\TYPE {mem' : ('a -> 'b -> bool) -> 'a -> 'b list -> bool}
\SYNOPSIS
Tests if an element is equivalent to a member of a list w.r.t. some relation.
\DESCRIBE
If {r} is a binary relation, {x} an element and {l} a list, the call
{mem' r x l} tests if there is an element in the list {l} that is equivalent to
{x} according to {r}, that is, if {r x x'} holds for some {x'} in {l}. The
function {mem} is the special case where the relation is equality.
\FAILURE
Fails only if the relation {r} fails.
\EXAMPLE
{
# mem' (fun x y -> abs(x) = abs(y)) (-1) [1;2;3];;
val it : bool = true
# mem' (fun x y -> abs(x) = abs(y)) (-1) [2;3;4];;
val it : bool = false
}
\USES
Set operations modulo some equivalence such as alpha-equivalence.
\SEEALSO
insert', mem, subtract', union', unions'.
\ENDDOC
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