Curry's Paradox

Prove anything! Without using negation or contradiction! Let P be P->Q, where Q is whatever you want to prove. A proof that Q (with no assumptions):

1. P->P (Identity)

2. P->(P->Q) (Substitution)

3. P->Q (Contraction)

4. P (Substitution)

5. Q (3 and 4 and Modus Ponens)