more changes to intro
more changes to intro

rlewis1988/logic_and_proof,rlewis1988/logic_and_proof,rlewis1988/logic_and_proof,leanprover/logic_and_proof,leanprover/logic_and_proof,avigad/logic_and_proof,avigad/logic_and_proof,avigad/logic_and_proof,leanprover/logic_and_proof