YES (VAR x0 x1 y x z) (RULES f(i(x0),f(x0,x1)) -> x1 f(i(x0),x0) -> e() i(i(x0)) -> x0 f(x1,f(i(x1),x0)) -> x0 i(e()) -> e() i(f(y,x)) -> f(i(x),i(y)) f(e(),x) -> x f(x,e()) -> 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 + 1 i_A(x1) = x1 e_A = 1 f#_A(x1,x2) = x1 e#_A = 0 and precedence: i > f > e )