data TermPr = Atom String | Var String |
              Apply String [TermPr]


instance Show TermPr where

   show (Atom s)     = s
   show (Var s)      = s
   show (Apply s ls) = s++"("++(showarg ls)
                 where
     showarg (t:[])    = (show t)++")"
     showarg (t:ts)    = (show t)++","++(showarg ts)