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                'use strict';
class ruleSet {
  constructor() { = [];
  public get rules() {
  public insertRule(first, second) {
    if (this._allowRule(first, second)) {
      this._addRule(first, second);  
  private _allowRule(newFirst, newSecond) {
    // Circular path and escape from recursion, or if input invalid
    if (newFirst === newSecond || !newFirst || !newSecond) {
        return false;

    // loop through current data 
    for (const [existingFirst, existingSecond] of {

      // If we can chain to another rule, 
      // test its second value to see if it creates a loop with our first
      if (newSecond === existingFirst) {  
        return this._allowRule(newFirst, existingSecond);

    return true;
  private _addRule(first, second) {[first, second]);

const mySet = new ruleSet();

mySet.insertRule(1, 2); // pass
mySet.insertRule(2, 1); // fail
mySet.insertRule(2, 3); // pass
mySet.insertRule(2, 5); // pass
mySet.insertRule(3, 1); // fail
mySet.insertRule(4, 4); // fail
mySet.insertRule(4); // fail