docs: function(obj) {
      console.log(`trained in ${ obj.iterations } iterations with error: ${ obj.error }`);
  
      const result01 = net.run([0, 1]);
      const result00 = net.run([0, 0]);
      const result11 = net.run([1, 1]);
      const result10 = net.run([1, 0]);
  
      assert(result01[0] > 0.9);
      assert(result00[0] < 0.1);
      assert(result11[0] < 0.1);
      assert(result10[0] > 0.9);
  
      console.log('0 XOR 1: ', result01);  // 0.987
      console.log('0 XOR 0: ', result00);  // 0.058
      console.log('1 XOR 1: ', result11);  // 0.087
      console.log('1 XOR 0: ', result10);  // 0.934
    }