plus 0 x x plus s x y s plus p s x y times 0 y 0 times s x y plus y times p s x y p s 0 0 p s s x s p s x fac 0 x x fac s x y fac p s x times s x y factorial x fac x s 0 plus 2 0 0 s 1 p 1 times 2 fac 2 factorial 1 FULL ./TRS/Thiemann/factorial1.trs