sort the list without changing the original list, therefore, the order of the...

sort the list without changing the original list, therefore, the order of the standard answer doesn't change in proof tree

src/components/ProofStepDialog.vue

@@ -211,13 +211,13 @@ export default {
       this.standardAnswer = this.standardAnswer.map(answer => ast.astsToString(answer));
 
       // sort the list for comparison
-      this.standardAnswer.sort();
-      this.answers.sort();
+      const standardAnswerSorted = this.standardAnswer.toSorted();
+      const answersSorted = this.answers.toSorted();
 
-      for (let i = 0; i < this.standardAnswer.length; i++) {
-        const output = validator(this.standardAnswer[i], this.answers[i]);
+      for (let i = 0; i < standardAnswerSorted.length; i++) {
+        const output = validator(standardAnswerSorted[i], answersSorted[i]);
         if (!output[0]) {
-          this.errorMsg = "Incorrect answer in statement " + this.answers[i] + output[1];
+          this.errorMsg = "Incorrect answer in statement " + answersSorted[i] + output[1];
           return;
         }
       }