Better documentation for mkEtaWW
So that hopefully I understand it faster next time. Also got rid of the
confusing orig_expr, which makes the call site in etaExpand look out
of sync with the passed n (which is not the original n).
So that hopefully I understand it faster next time. Also got rid of the
confusing orig_expr, which makes the call site in etaExpand look out
of sync with the passed n (which is not the original n).