 Using Levien seminal works, many other implementations of the Metamath design principles have been implemented for a broad variety of languages.Juha Arpiainen has implemented his own proof checker in Common Lisp called Bourbaki and Marnix Klooster has coded a proof checker in Haskell called "Hmm".Although they all use the overall Metamath approach to formal system checker coding, they also implement new concepts of their own.