 As of July 2019, the set of proved theorems using Metamath is one of the largest bodies of formalized mathematics, containing in particular proofs of 71 of the 100 theorems of the "Formalizing 100 Theorems" challenge, making it third after HOL Light and Isabelle, but before Coq, Mizar, ProofPower, Lean, Nqthm, ACL2, and Nuprl.There are at least 17 proof verifiers for databases that use the Metamath format.The Metamath language is a metalanguage, suitable for developing a wide variety of formal systems.