subtract' : ('a -> 'a -> bool) -> 'a list -> 'a list -> 'a list
Subtraction of sets modulo an equivalence.
The call subtract' r l1 l2 removes from the list l1 all elements x such
that there is an x' in l2 with r x x'. If l1 and l2 were free of
equivalents under r, the resulting list will be too, so this is a set
operation modulo an equivalence. The function subtract is the special case
where the relation is just equality.
- FAILURE CONDITIONS
Fails only if the function r fails.
# subtract' (fun x y -> abs(x) = abs(y)) [-1; 2; 1] [-2; -3; 4; -4];;
val it : int list = [-1; 1]
Maintaining sets modulo an equivalence such as alpha-equivalence.
- SEE ALSO
insert', mem', union, union', unions'.