Backtracking fixed

src/prolog/builtins/arithmeticOperators.kt

@@ -39,6 +39,10 @@ class EvaluatesToDifferent(private val left: Expression, private val right: Expr
         }
     }
 
+    override fun applySubstitution(subs: Substitutions): EvaluatesToDifferent = EvaluatesToDifferent(
+        left.applySubstitution(subs) as Expression,
+        right.applySubstitution(subs) as Expression
+    )
 }
 
 /**
@@ -57,6 +61,11 @@ class EvaluatesTo(private val left: Expression, private val right: Expression) :
 
         return if (equivalent(t1.to, t2.to, subs)) sequenceOf(Result.success(emptyMap())) else emptySequence()
     }
+
+    override fun applySubstitution(subs: Substitutions): EvaluatesTo = EvaluatesTo(
+        left.applySubstitution(subs) as Expression,
+        right.applySubstitution(subs) as Expression
+    )
 }
 
 /**
@@ -78,6 +87,11 @@ class Is(val number: Expression, val expr: Expression) :
 
         return unifyLazy(t1.to, t2.to, subs)
     }
+
+    override fun applySubstitution(subs: Substitutions): Is = Is(
+        number.applySubstitution(subs) as Expression,
+        expr.applySubstitution(subs) as Expression
+    )
 }
 
 /**
@@ -101,6 +115,11 @@ open class Add(private val expr1: Expression, private val expr2: Expression) :
         val simplification = result.simplify(map.first().getOrThrow())
         return Simplification(this, simplification.to)
     }
+
+    override fun applySubstitution(subs: Substitutions): Add = Add(
+        expr1.applySubstitution(subs) as Expression,
+        expr2.applySubstitution(subs) as Expression
+    )
 }
 
 /**
@@ -114,6 +133,11 @@ open class Subtract(private val expr1: Expression, private val expr2: Expression
         val simplification = result.simplify(map.first().getOrThrow())
         return Simplification(this, simplification.to)
     }
+
+    override fun applySubstitution(subs: Substitutions): Subtract = Subtract(
+        expr1.applySubstitution(subs) as Expression,
+        expr2.applySubstitution(subs) as Expression
+    )
 }
 
 /**
@@ -127,6 +151,11 @@ class Multiply(val expr1: Expression, val expr2: Expression) :
         val simplification = result.simplify(map.first().getOrThrow())
         return Simplification(this, simplification.to)
     }
+
+    override fun applySubstitution(subs: Substitutions): Multiply = Multiply(
+        expr1.applySubstitution(subs) as Expression,
+        expr2.applySubstitution(subs) as Expression
+    )
 }
 
 class Divide(private val expr1: Expression, private val expr2: Expression) :
@@ -137,6 +166,11 @@ class Divide(private val expr1: Expression, private val expr2: Expression) :
         val simplification = result.simplify(map.first().getOrThrow())
         return Simplification(this, simplification.to)
     }
+
+    override fun applySubstitution(subs: Substitutions): Divide = Divide(
+        expr1.applySubstitution(subs) as Expression,
+        expr2.applySubstitution(subs) as Expression
+    )
 }
 
 // TODO Expr mod Expr
@@ -166,5 +200,11 @@ class Between(private val expr1: Expression, private val expr2: Expression, priv
         }
     }
 
+    override fun applySubstitution(subs: Substitutions): Between = Between(
+        expr1.applySubstitution(subs) as Expression,
+        expr2.applySubstitution(subs) as Expression,
+        expr3.applySubstitution(subs) as Expression
+    )
+
     override fun toString(): String = "$expr1..$expr3..$expr2"
 }