YES (VAR x1 x0 x y z) (RULES i(f(x1,x0)) -> f(i(x0),i(x1)) f(i(x0),e()) -> i(x0) f(i(x1),f(x1,x0)) -> x0 i(i(x0)) -> f(x0,e()) f(x1,f(i(x1),x0)) -> x0 i(e()) -> e() f(e(),x) -> x f(x,i(x)) -> e() f(f(x,y),z) -> f(x,f(y,z)) ) (COMMENT Termination is shown by ELPO with interpretations on natural numbers f_A(x1,x2) = x1 + x2 i_A(x1) = x1 e_A = 0 e#_A = 0 and precedence: i > f > e )