I believe the problem is "the shirt worn by Bob". This syntax isn't
supported, because Bob could conceivably be wearing any number of
shirts, including zero. Try something like:
<code>
if Bob is wearing a shirt (called the top) and Bob is wearing pants
(called the bottom) and the color of the top is the color of the
bottom:
</code>
If he does happen to be wearing multiple shirts or pants, this will
only check the first one of each. Presumably that won't happen, but if
it does and you need to handle that case, you could do something like
this:
<code>
Color-matching relates a thing (called X) to a thing (called Y) when
the color of X is the color of Y. The verb to color-match (it color-
matches, they color-match, it color-matched, it is color-matched, it
is color-matching) implies the color-matching relation.
[...]
if Bob is wearing a shirt that color-matches pants worn by Bob:
</code>
vw
Aha! That makes perfect sense. Thank you for clearing that up.