diff --git a/src/ast.rs b/src/ast.rs
index ef19a04..9f81d17 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -1,4 +1,4 @@
-#[derive(PartialEq)]
+#[derive(Eq, Hash, PartialEq)]
 pub struct PredicateDeclaration
 {
 	pub name: String,