17: fix some typos and add some clarifications
17: fix some typos and add some clarifications

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