Enable check box

Hello commcare users
I have a check box field with the following values on food consommed

  1. Rice
  2. water
  3. milk
  4. Nothing
    I would like to diseable “Nothing” when I select rice, water or milk
    How can I do it?
    Your help please!
    Felix

Use the below formula under Validation Condition of question

not(selected(., ‘Nothing’) and count-selected(.) > 1)

this will not let user select Nothing if the user selects any of 1 to 3 options

Perfect. Thanks a lot for the support!!!
Felix