New revision: My last solution works with just one Room/Building at once. If you want to add more and check if they are all reserved or bookable, I have fixed the code in that manner:AND([Start] < [End],[End] < [Start]+1,ISBLANK(INTERSECT( [_THISROW]...

Hi @Steve, finally I have understood your tip and I re-wrote the code like this:AND([Start] < [End],[End] < [Start]+1,NOT(IN( [_THISROW].[MultiBuilding],SELECT(Reservation[MultiBuilding],AND(([Key] <> [_THISROW].[Key]),[Start] < [_THISROW].[End],[_TH...

Thank you @Steve!

Hi @Joseph_Seddik, recently I added another condition to that filter:FILTER(Reservation,AND(IN([_THISROW].[Key], [MultiBuilding]),[Start] >= TODAY()))Because I want that the app shows me only the future reservations. I don't understand why I can see ...

@Joseph_Seddik you saved me again! Thank you very much!Yesterday, I tried a solution similar:FILTER(Reservation, IN([_THISROW].[RoomID], Reservation[MultiRoom])I need to study it deeper, sure for me, Google Apps Script is easier to understand than Ap...