Homework 6

Due Thursday, March 16 at the start of class.

Prove the following sequents using only Peano's axioms:

1. |- -(0'=0'')
2. |- 0'''×0''=0''''''
3. |- a×(b+c)=(a×b)+(a×c) (you may use the associativity sequent |- a+(b+c)=(a+b)+c)
4. (extra credit) |- a×(b×c)=(a×b)×c