I have encountered the following pigeonhole principle problem. I'm not sure what the question means, so I would like to clarify what it means:
17 rooks are placed on an 8×8 chessboard. Prove that there are at least 3 rooks that do not threaten each other.
What does it mean that 3 rooks do not threaten each other? Does it mean that there is a set of 3 rooks such that no pair involving any of the 3 rooks, involve two rooks that threaten each other? Or does it mean that there are 3 pairs of rooks, the pairs consisting of any 2 rooks, such that in the pair, the rooks do not threaten each other? Or does it mean something else entirely?
Could I get an explanation of what the question means (please avoid any hints/solutions)? Thanks so much in advance!