I am explaining something that has the following structure if written in computer language:
if X A else B
However the condition
X is quite subtle, and because of this I want to recall it when I state the else statement.
Before adding this extra explanation I had an otherwise in place of my else.
I was wondering if it was proper to keep the otherwise, making the fragment read as follows:
If [X] then [A]. Otherwise if [Y] [B]
I want to insist that [Y] is the strict opposite of [X] here.
Even though I am not authorized to publish the exact citation, I will try to write something "equivalent":
If x is not in X then A happens. Otherwise if x is in X then B happens.