The Proofchecker is a heuristically oriented computer program for checking mathematical proofs, with the checking of textbook proofs as its ultimate goal. It constructs, from each proof step given to it, a corresponding sequence of formal steps, if possible. It records the current state of the proof in the form of what it is sufficient to prove. There are two logical rules of inference: modus powers and insertion (if it is sufficient to prove B, and A is the theorem, then it is sufficient to prove A implies B). The permissible formal steps include these rules of inference as well as provision for handling definitions, lemmas, calculations, and reversion to previous states. As of now, most of the formalisms are programmed and partially debugged, but the heuristic aspects have yet to be programmed.