I think for games with an uncertain number of ins and outs, or with fewer spots than we have variables, it's critical to pay attention to the outs as well as the ins.
We also notice that the first rule sets up two possible states of the world, one in which q is in, and one in which Q is out. If q is in then t is in. However, in the world where q is out, q is filling our only out slot. So, in the two possible states of the world, T is in in both. So t must always be in.
