1. (a->(b->c))->((a->b)->(a->c)) (axiom 2) 2. (a->(b->a))->((a->b)->(a->a)) (replace c with a in (1)) 3. a->(b->a) (axiom 1) 4. (a->b)->(a->a) (2, 3, M.P.) 5. (a->(b->a))->(a->a) (replace b with b->a in (4)) 6. a->a (5, 3, M.P.)