The WildFunction is simulating an applied function with args, matching (in this case) something like f(x, y). So `F.nargs = f(x,y).nargs`...but perhaps one should be able to define it as (1, 2) and have it match either a 1 or 2 arg function. I'm not sure how the match works. But since the match in the doctest works I guess what was done is ok.