YES (VAR x0 x1 x y z) (RULES f(f(x0,i(a())),i(a())) -> f(f(x0,a()),a()) f(f(x0,i(a())),b()) -> f(f(x0,b()),a()) f(i(a()),i(a())) -> f(a(),a()) i(f(x1,x0)) -> f(i(x0),i(x1)) f(i(x0),x0) -> e() i(e()) -> e() f(f(x0,i(x1)),x1) -> x0 f(i(a()),b()) -> f(b(),a()) i(i(x1)) -> x1 i(b()) -> b() f(f(f(x0,a()),a()),a()) -> f(x0,i(a())) f(f(a(),a()),a()) -> i(a()) f(e(),x0) -> x0 f(f(x0,a()),b()) -> f(f(x0,b()),i(a())) f(f(x0,x1),i(x1)) -> x0 f(f(x0,b()),b()) -> x0 f(a(),b()) -> f(b(),i(a())) f(b(),b()) -> e() f(x,e()) -> x f(x,i(x)) -> e() f(x,f(y,z)) -> f(f(x,y),z) ) (COMMENT Termination is shown by EKBO with interpretations on natural numbers f_A(x1,x2) = x1 + x2 + 1 i_A(x1) = x1 e_A = 1 a_A = 1 b_A = 5 f#_A(x1,x2) = x2 e#_A = 0 a#_A = 0 b#_A = 0 weights w0 = 1 w(f) = 0 w(i) = 0 w(e) = 1 w(a) = 2 w(b) = 3 and precedence: i > b > f > e > a )