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Oct 26, 2018 at 16:26 comment added Axel Dahlberg I've re-written the question, I hope it's more clear now.
Oct 26, 2018 at 15:52 comment added Axel Dahlberg $X$ is not part of the input. For the problem counting the number of orbits the input is simply the number of vertices $n$ and $X$ is then the graphs on $n$ vertices. For deciding the size of an orbit the input is a graph (element of $X$). I can rewrite the question for the case where $X$ are graphs if that's clearer.
Oct 26, 2018 at 15:00 comment added Keith Kearnes I mean: what is the input to your original problem about groups acting on sets? Is $X$ part of the input? If so, then $X$ cannot be exponentially large in terms of the input (it is part of the input). So what is the input?
Oct 26, 2018 at 14:20 comment added Axel Dahlberg Sorry for being unclear. In the case of graphs, the input is the number of vertices.
Oct 26, 2018 at 14:06 comment added Keith Kearnes What is the input?
Oct 26, 2018 at 14:04 comment added Axel Dahlberg The size of the orbits can be exponentially large in the input of the problem. So even if finding the orbits can exponentially long time, deciding their size can still be in $P$. No $X$ is finite but exponentially large in the input of the problem. $X$ can for example be all graphs on a fixed number of vertices or all words of a certain length with entries from a finite alphabet.
Oct 26, 2018 at 13:42 history edited Keith Kearnes CC BY-SA 4.0
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Oct 26, 2018 at 13:39 history undeleted Keith Kearnes
Oct 26, 2018 at 13:37 history deleted Keith Kearnes via Vote
Oct 26, 2018 at 13:37 history answered Keith Kearnes CC BY-SA 4.0