AbstractThe semantics of a proof language relies on the representation of the state of a proof after a logical rule has been applied. This information, which is usually meaningless from a logical point of view, is fundamental to describe the control mechanism of the proof search provided by the language. In this paper, we present a monadic datatype to represent the state information of a proof and we illustrate its use in the PVS theorem prover. We show how this representation can be used to design a new set of powerful tacticals for PVS, called PVS#, that have a simpler and clearer semantics compared to the semantics of standard PVS tacticals.