code: function includesBothInAGroup(groups, left, right) {
      return groups.some(group => group.indexOf(left) !== -1 && group.indexOf(right) !== -1);
  }
docs: Checks whether any group which includes both given operator exists or not.
  
  @param {Array.<string[]>} groups - A list of groups to check.
  @param {string} left - An operator.
  @param {string} right - Another operator.
  @returns {boolean} `true` if such group existed.