Simplified the code, removed first_arg, the Option

src/forms.rs

@@ -332,13 +332,6 @@ pub enum PredicateClause {
 }
 
 impl PredicateClause {
-    pub fn first_arg(&self) -> Option<&Term> {
-        match self {
-            &PredicateClause::Fact(ref term, ..) => term.first_arg(),
-            &PredicateClause::Rule(ref rule, ..) => rule.head.1.first().map(|bt| bt.as_ref()),
-        }
-    }
-
     // TODO: add this to `Term` in `prolog_parser` like `first_arg`.
     pub fn args(&self) -> Option<&[Box<Term>]> {
         match *self {