docs: function (f, x) {
          var integral = function (a, b) {
              var tenx = Math.pow(10, x),
                  sum = 0,
                  i;
  
              for (i = a + (1 / tenx); i < b; i += 1 / tenx) {
                  sum += f(i) / tenx;
              }
  
              return Math.round(sum * tenx / 10) / (tenx / 10);
          };
  
          integral.from = integral;
          return integral;
      }