nd for fol: typo from Dan Velleman
nd for fol: typo from Dan Velleman

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