1 abstract class Term

     2 case class Var(s: String) extends Term

     3 case class Consts(s: String) extends Term

     4 case class Fun(s: String, ts: List[Term]) extends Term

     5 

     6 abstract class Form

     7 case object True extends Form

     8 case object False extends Form

     9 case class And(f1: Form, f2: Form) extends Form

    10 case class Or(f1: Form, f2: Form) extends Form

    11 case class Imp(f1: Form, f2: Form) extends Form

    12 case class Neg(f: Form) extends Form

    13 case class Pred(s: String, ts: List[Term]) extends Form