The Fate Core System rulebook states on p. 71 (Compelling Aspects):
Finally, and this is very important: if a player wants to compel another character, it costs a fate point to propose the complication. The GM can always compel for free, and any player can propose a compel on his or her own character for free.
If you compel another character with an aspect that isn't attached to that character (like a game or situation aspect), do you still pay this cost? Do you pay the cost when compelling NPCs or only other PCs? My reading is that it's for all aspects and characters, but I'm not sure.
I'm also having some difficulty with this similar rule in Fate Accelerated, p. 27 (Invoking Aspects):
PvP: The only time that fate point might not go to the GM is when you’re in conflict with another player. If you are, and you invoke one of that player’s character aspects to help you out against them, they will get the fate point instead of the GM once the scene is over.
There's a corresponding rule on Fate Core System, p. 81 (Earning Fate Points):
Have Your Aspects Invoked Against You: If someone pays a fate point to invoke an aspect attached to your character, you gain their fate point at the end of the scene. This includes advantages created on your character, as well as consequences.
I have roughly the same questions about this rule: Does it only apply to character aspects and consequences, or to all aspects? Can the GM earn points this way or only the players?
In this case, my reading is that “attached” aspects do not include game or situation aspects, and only players can earn fate points this way, but I'm not sure. If it does apply to GMs, does that mean they carry the point over into the next scene? I'm guessing it doesn't work that way, since it's not one of the two exceptions listed on p. 82.