MAYBE

Problem:
 a(h(),h(),h(),x) -> s(x)
 a(l,x,s(y),h()) -> a(l,x,y,s(h()))
 a(l,x,s(y),s(z)) -> a(l,x,y,a(l,x,s(y),z))
 a(l,s(x),h(),z) -> a(l,x,z,z)
 a(s(l),h(),h(),z) -> a(l,z,h(),z)
 +(x,h()) -> x
 +(h(),x) -> x
 +(s(x),s(y)) -> s(s(+(x,y)))
 +(+(x,y),z) -> +(x,+(y,z))
 s(h()) -> 1()
 app(nil(),k) -> k
 app(l,nil()) -> l
 app(cons(x,l),k) -> cons(x,app(l,k))
 sum(cons(x,nil())) -> cons(x,nil())
 sum(cons(x,cons(y,l))) -> sum(cons(a(x,y,h(),h()),l))

Proof:
 Open