Return a list of all the elements present in the leftList and not
in the rightList. Return in the order of their appearance in leftList.
Uses the comparison built into Set membership (SameValueZero)
which is like JavaScript's === except that it judges any NaN to
be the same as any NaN and it judges 0 to be the same a -0.
This is often used on lists of names that should match, in order to generate
useful diagnostics about the unmatched names.
Return a list of all the elements present in the
leftListand not in therightList. Return in the order of their appearance inleftList. Uses the comparison built intoSetmembership (SameValueZero) which is like JavaScript's===except that it judges anyNaNto be the same as anyNaNand it judges0to be the same a-0.This is often used on lists of names that should match, in order to generate useful diagnostics about the unmatched names.