fix: Evaluation

src/prolog/components/terms/Variable.kt

@@ -21,18 +21,18 @@ data class Variable(val name: String) : Term {
         alias = Optional.empty()
     }
 
-    override fun toString(): String {
-        return when {
-            alias.isPresent -> "$name = ${alias.get()}"
-            else -> name
+    override fun compareTo(other: Term): Int {
+        return when (other) {
+            is Variable  -> name.compareTo(other.name)
+            // Variables are always less than atoms
+            else         -> -1
         }
     }
 
-    override fun equals(other: Any?): Boolean {
-        return if (alias.isPresent) {
-            alias.get() == other
-        } else {
-            name == other.toString()
+    override fun toString(): String {
+        return when {
+            alias.isPresent -> "$name: ${alias.get()}"
+            else -> name
         }
     }
 }