enable and disable data in enum List, according to the selected value

[Adolfo_Enrique_]

Hello everyone, please I need to solve the following situation.
I have created an enumList with the values ​​A, A1 , B, B1.
I need to perform the following Validation, For example If the user has selected the value A, A1 must be disabled to be selected, otherwise if he selects A1, A must be disabled for the selection. Same for B and B1.

It is possible to perform this validation.
I hope your help, thank you very much.

[Steve]

You'll need to use Valid If expressions to construct the allowed lists:

Drop-down from Valid_If - AppSheet Help