I get thrown by some of the phrasing. For example, the Feb '99 tree game's last 2 rules. This is my best stab at diagramming them. Does anyone have a definitive diagram for these rules?
If yews are not in the park, then either laurels or oaks, but not both, are in the park.
Not Y --> (L --> Not O) and (O-->Not L)
This isn't quite right. You're saying here that Yews not being in the park creates two conditional relationships, which it does. If you have Y, you need to have L or O, but you can't have both. With this rule, L, O, and Y could ALL be out of the park.
.....or is it
Not Y --> L<-|->O
Not quite right again, for the same reason. In fact, this is the shorthand for the first one you wrote above, so they're logically equivalent.
I'd diagram it as (~ stands in for 'not'):
~Y-> (L or O) and (~L or ~O)
If you don't have Y, then you have at least one of L and O (L or O), but you don't have both L and O (~L or ~O).
If it is not the case that the park contains both laurels and oaks, then it contains firs and spruces.
L<-|->O --> F AND S
Is "if it is not the case that both L and O" just another way of saying "L or O, but not both?"
This might be the meanest rule ever written. Your diagram means, "If L and O can't both be in the park, the F and S are in the park." Again, you have a sufficient condition that is itself a logical rule, which isn't the case here.
Let's take it part by part (which is what you should do for tricky rules):
"If it is not the case that the park contains both laurels and oaks..."
It's saying here that at least one of these two is NOT in the park, so my sufficient condition is "~L or ~O" - that just means one is definitely out (and both could be out).
"...then it contains firs and spruces."
Easy enough - "F and S"
So we get:
~L or ~O -> F and S
~F or ~S-> L and O
1) F and S are in
2) L and O are in
3) All 4 are in
But as soon as one of those four is Out of the park, we know that two others are definitely in. 3 seems like an outlier to me that's likely to show up on one question to make sure you didn't miss it.