library 
   BOOLEAN, NATURAL
endlib 

type BIT is
   sorts BIT 
   opns 0 (*! constructor *),
        1 (*! constructor *) : -> BIT
        not : BIT -> BIT
   eqns
      ofsort BIT
         not (0) = 1;
         not (1) = 0;
endtype

type MESSAGES is NATURAL renamedby
   sortnames MSG for NAT
endtype