Use the same api for imp::Term as for Term
diff --git a/src/lib.rs b/src/lib.rs
index 6556c97..3f9d57a 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -242,11 +242,11 @@
 
 impl Term {
     pub fn intern(string: &str) -> Term {
-        Term(string.into())
+        Term(imp::Term::intern(string))
     }
 
     pub fn as_str(&self) -> &str {
-        &self.0
+        self.0.as_str()
     }
 }