Backtracking fixed

src/prolog/logic/unification.kt

@@ -15,19 +15,15 @@ import prolog.ast.terms.*
 
 // Apply substitutions to a term
 fun applySubstitution(term: Term, subs: Substitutions): Term = when {
-    term is Fact -> {
-        Fact(applySubstitution(term.head, subs) as Head)
-    }
+    term is Fact -> term.applySubstitution(subs)
 
     variable(term, emptyMap()) -> {
         val variable = term as Variable
         subs[variable]?.let { applySubstitution(term = it, subs = subs) } ?: term
     }
+
     atomic(term, subs) -> term
-    compound(term, subs) -> {
-        val structure = term as Structure
-        Structure(structure.name, structure.arguments.map { applySubstitution(it, subs) })
-    }
+    compound(term, subs) -> term.applySubstitution(subs)
 
     else -> term
 }