MAYBE

Problem:
 app(app(minus(),0()),y) -> 0()
 app(app(minus(),app(s(),x)),0()) -> app(s(),x)
 app(app(minus(),app(s(),x)),app(s(),y)) -> app(app(minus(),x),y)
 app(app(le(),0()),y) -> true()
 app(app(le(),app(s(),x)),0()) -> false()
 app(app(le(),app(s(),x)),app(s(),y)) -> app(app(le(),x),y)
 app(app(app(if(),true()),x),y) -> x
 app(app(app(if(),false()),x),y) -> y
 app(perfectp(),0()) -> false()
 app(perfectp(),app(s(),x)) -> app(app(app(app(f(),x),app(s(),0())),app(s(),x)),app(s(),x))
 app(app(app(app(f(),0()),y),0()),u) -> true()
 app(app(app(app(f(),0()),y),app(s(),z)),u) -> false()
 app(app(app(app(f(),app(s(),x)),0()),z),u) ->
 app(app(app(app(f(),x),u),app(app(minus(),z),app(s(),x))),u)
 app(app(app(app(f(),app(s(),x)),app(s(),y)),z),u) ->
 app(app(app(if(),app(app(le(),x),y)),app(app(app(app(f(),app(s(),x)),app(app(minus(),y),x)),z),u)),
     app(app(app(app(f(),x),u),z),u))
 app(app(map(),fun),nil()) -> nil()
 app(app(map(),fun),app(app(cons(),x),xs)) -> app(app(cons(),app(fun,x)),app(app(map(),fun),xs))
 app(app(filter(),fun),nil()) -> nil()
 app(app(filter(),fun),app(app(cons(),x),xs)) -> app(app(app(app(filter2(),app(fun,x)),fun),x),xs)
 app(app(app(app(filter2(),true()),fun),x),xs) -> app(app(cons(),x),app(app(filter(),fun),xs))
 app(app(app(app(filter2(),false()),fun),x),xs) -> app(app(filter(),fun),xs)

Proof:
 Open