YES (VAR x1 x0 x y z) (RULES i(f(x1,x0)) -> f(i(x0),i(x1)) f(f(x0,i(x1)),x1) -> x0 f(i(x0),x0) -> e() i(i(x0)) -> x0 i(e()) -> e() f(e(),x0) -> x0 f(f(x0,x1),i(x1)) -> x0 f(x,e()) -> x f(x,i(x)) -> e() f(x,f(y,z)) -> f(f(x,y),z) ) (COMMENT Termination is shown by ELPO with interpretations on natural numbers f_A(x1,x2) = x1 + x2 + 1 i_A(x1) = x1 e_A = 1 f#_A(x1,x2) = x2 e#_A = 0 and precedence: i > f > e )