A colleague and I are trying to figure out if the following statement is true and if so, which mathematical theorem and formulations are the one that apply here:
Given a hotel with N rooms of the same type. If for every day of a proposed reservation there is at least 1 room that is available. Then no matter what the other reservations are over that time period, I can arrange them so that the new reservation is made continuously on the same room.
When looking only at 2 rooms, this seems true:

And "playing around with rectangles", it seems fine with more rooms too:

But we're curious to see if there's a formal definition of this problem and a proof or cases that disprove this because so far all we have is "an intuition that this seems true".