 Instead, it can simply be regarded as a way to prove that inference rules (asserted as axioms or proven later) can be applied.The largest database of proved theorems follows conventional ZFC set theory and classic logic, but other databases exist and others can be created.The Metamath language design is focused on simplicity; the language, employed to state the definitions, axioms, inference rules and theorems is only composed of a handful of keywords, and all the proofs are checked using one simple algorithm based on the substitution of variables (with optional provisos for what variables must remain distinct after a substitution is made).