Checkpoint

src/prolog/logic/arithmetic.kt

@@ -58,7 +58,7 @@ fun succ(term1: Expression, term2: Expression, subs: Substitutions): Answers {
             it.fold(
                 onSuccess = { result ->
                     val t1 = applySubstitution(term1, result)
-                    if (t1 in result) {
+                    if (t1 in result || t1 in result.values) {
                         val e1 = t1.simplify(result)
                         if (e1.to is Integer && e1.to.value < 0) {
                             return@sequence

src/prolog/logic/unification.kt

@@ -13,7 +13,15 @@ import prolog.ast.arithmetic.Float
 
 // Apply substitutions to a term
 fun applySubstitution(term: Term, subs: Substitutions): Term = when {
-    variable(term, emptyMap()) -> subs[(term as Variable)] ?: term
+    variable(term, emptyMap()) -> {
+        var result = subs[(term as Variable)]
+
+        while (result != null && result is Variable && result in subs) {
+            result = subs[result]
+        }
+
+        result ?: term
+    }
     atomic(term, subs) -> term
     compound(term, subs) -> {
         val structure = term as Structure
@@ -25,7 +33,7 @@ fun applySubstitution(term: Term, subs: Substitutions): Term = when {
 
 //TODO Combine with the other applySubstitution function
 fun applySubstitution(expr: Expression, subs: Substitutions): Expression = when {
-    variable(expr, subs) -> applySubstitution(expr as Term, subs) as Expression
+    variable(expr, emptyMap()) -> applySubstitution(expr as Term, subs) as Expression
     atomic(expr, subs) -> expr
     expr is LogicOperator -> {
         expr.arguments = expr.arguments.map { applySubstitution(it, subs) }