User blog comment:Wythagoras/All my stuff/@comment-5150073-20130708161220

We can make a rule: f(a,b) = f(f(a,b-1),b-1) and we can do f(a,b) = f(f(f(a,b-1),b-1),b-1). We can continue with 4 nestings, 5, 6, and so on. You didn't specify the number of them, and there is a problem.