function _unequal (x, y) {
    return !equalScalar(x, y)
  }
Test whether two values are unequal.

The function tests whether the relative difference between x and y is
larger than the configured relTol and absTol. The function cannot be used to compare
values smaller than approximately 2.22e-16.

For matrices, the function is evaluated element wise.
In case of complex numbers, x.re must unequal y.re, or x.im must unequal y.im.
Strings are compared by their numerical value.

Values `null` and `undefined` are compared strictly, thus `null` is unequal
with everything except `null`, and `undefined` is unequal with everything
except `undefined`.

Syntax:

   math.unequal(x, y)

Examples:

   math.unequal(2 + 2, 3)       // returns true
   math.unequal(2 + 2, 4)       // returns false

   const a = math.unit('50 cm')
   const b = math.unit('5 m')
   math.unequal(a, b)           // returns false

   const c = [2, 5, 1]
   const d = [2, 7, 1]

   math.unequal(c, d)           // returns [false, true, false]
   math.deepEqual(c, d)         // returns false

   math.unequal(0, null)        // returns true
See also:

   equal, deepEqual, smaller, smallerEq, larger, largerEq, compare

@param  {number | BigNumber | Fraction | boolean | Complex | Unit | string | Array | Matrix | undefined} x First value to compare
@param  {number | BigNumber | Fraction | boolean | Complex | Unit | string | Array | Matrix | undefined} y Second value to compare
@return {boolean | Array | Matrix} Returns true when the compared values are unequal, else returns false