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                This problem was asked by Jane Street.

`cons(a, b)` constructs a pair, and `car(pair)` and `cdr(pair)` returns the first and last element of that pair. For example, `car(cons(3, 4)) returns 3, and cdr(cons(3, 4))` returns `4`.

Given this implementation of cons:
def cons(a, b):
    def pair(f):
        return f(a, b)
    return pair
Implement `car` and `cdr`.


                /* The given question assumes (requires?) python -- I honestly don't know what other languages include a Pair primitive. Since I'm focusing on JS and this is on codepen... I'm going to adjust this a bit to JS where cons constructs an object, car needs to get the key, and cdr needs to get the value. */

/*  This seemed easy so I'm assuming the difficulty with this is something specific to pairs in Python?  Was thinking I could use an array of two entries instead of an object, but my understanding of a pair is associating the two elements and in JS we do that with an object... and this wouldn't be any harder with an array.*/


                function cons(a,b){
  var pair = {};
  pair[a] = b;
  return pair;

function car( pair ){
  return Object.keys(pair)[0];

function cdr( pair ){
  return Object.values(pair)[0];