Here is a larger compendium of mathematical proofs that are formally proved all the way back to ZFC axioms using classical logic, namely the Metamath Proof Expl

Here is a larger compendium of mathematical proofs that are formally proved all the way back to ZFC axioms using classical logic, namely the Metamath Proof Explorer: http://us.metamath.org/mpeuni/mmset.html http://us.metamath.org/mpeuni/mmset.html Metamath lets you state your axioms including your logic system, so there are other Metamath proof databases that make different assumptions.