text: 'use strict';
  
  var assert = require('assert');
  
  function add (a, b) {
      if (!isNaN(a)) assert(0 < a);
      if (typeof b === 'number') {
          assert(0 < b);
      }
  
      if (typeof a === 'number')
          assert(0 < a);
      else if (typeof b === 'number')
          assert(0 < b);
      else
          assert(false);
  
      return a + b;
  }
  