Cleanup 3

src/prolog/builtins/arithmeticOperators.kt

@@ -122,6 +122,11 @@ open class Add(private val expr1: Expression, private val expr2: Expression) :
     )
 }
 
+class Plus(private val expr1: Expression, private val expr2: Expression, private val expr3: Expression) :
+    CompoundTerm("plus", expr1, expr2, expr3) {
+    override fun satisfy(subs: Substitutions): Answers = plus(expr1, expr2, expr3, subs)
+}
+
 /**
  * Result = Expr1 - Expr2
  */