feat(02): add sections on writing proofs, using shortcuts
feat(02): add sections on writing proofs, using shortcuts

leanprover/logic_and_proof,avigad/logic_and_proof,soonhokong/logic_and_proof,soonhokong/logic_and_proof,leanprover/logic_and_proof,soonhokong/logic_and_proof,rlewis1988/logic_and_proof,fpvandoorn/logic_and_proof,rlewis1988/logic_and_proof,rlewis1988/logic_and_proof,fpvandoorn/logic_and_proof,fpvandoorn/logic_and_proof,leanprover/logic_and_proof,avigad/logic_and_proof,avigad/logic_and_proof