is this possible?

you got 4 cells if one of the cell contains something u cant add anything in the other 3 cells, only when u delete the contain of the other cell.

Example
you got 4 cells A1, A2, A3 and A4
Cell A3 contains 20 and when u try to fill in something in cell A4 it gives and error (and say something like delete the contain of cell A3...)

can you do somthing like that?