Help making option feature mandatory

I have two option features and need to make either one mandatory  depending on the quantity  of  one of the option features.

I am trying to make an option feature ('Drawings'.'General Arrangements') mandatory only when it's Options are equal  to one and option feature ('Drawings'.'Not Available') mandatory otherwise

I have tried  to make a count of the items not excluded using the statement below, then  make the item  mandatory  using the count

CONTRIBUTE 1 TO 'P0P1 GEN'.'Drawings'.'Counter'
FOR ALL &var IN {OptionsOf('Drawings'.'General Arrangements')}
WHERE &var.state() = true

Can anyone help  please