parts of x.

HT: However, what happens when you complicate
    the scenario so as to describe components
    which interact?

As things stand, it would be complicating the
scenario a bit just to posit components for x,
for example, as depicted in the following way:

                         x              y
                         o-------------&gt;o
                        ...            /|\
                       . . .          / | \
                      .  .  .        /  |  \
                     .   .