Backtracking fixed

src/prolog/ast/logic/Rule.kt

@@ -1,6 +1,13 @@
 package prolog.ast.logic
 
+import prolog.Substitutions
 import prolog.ast.terms.Body
 import prolog.ast.terms.Head
+import prolog.logic.applySubstitution
 
-class Rule(head: Head, body: Body) : Clause(head, body)
+class Rule(head: Head, body: Body) : Clause(head, body) {
+    override fun applySubstitution(subs: Substitutions): Rule = Rule(
+        head = applySubstitution(head, subs) as Head,
+        body = applySubstitution(body, subs) as Body
+    )
+}