The vsprite and bob structures must point to one another, so that the
system can find the entire GEL.  The structures are linked with statements
like this:

    myBob.BobVSprite = &myVSprite;
    myVSprite.VSBob  = &myBob;

Now the system (and the application program) can go back and forth between
the two structures to obtain the various bob variables.