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