code: function rightIdentity(f) {
      var M = f();
  
      return forAll(_.Int).satisfy(function(a) {
        var m = M.of(a);
  
        return m.chain(M.of).isEqual(m);
      });
    }
docs: /*
  2nd Law: Right Identity
  'm.chain(m.of)' is equivalent to 'm'