text: /*DOCSTRING: HELPER FUNCTION to Compute the unique vocabulary set of a corpus.*/
  module.exports = (function()
  {
    Set.prototype.__arrUnion = function(arr)
    {
      arr.forEach(this.add, this); //'this' refers to the Set that called the method here.
    }
  
    return function(matr) // For a given 2D array, returns the set union of its elements.
           {
            var unionOfVector = new Set();
            matr.forEach(unionOfVector.__arrUnion, unionOfVector); //union in-place
            return unionOfVector;
           };
  
  })();
  