I want a unit to appear only if a certain other is not present.
For example, I have a T-55 with a 50% probability of presence. I have another T-72 with a 100% probability of presense; however, I want the T-72 to exist ONLY is the T-55 is NOT present.
The end result will be either a T-55 or a T-72, but not both.
Does anyone know how to do this? I understand that the term "Alive" applies here, but I'm not sure how to use it in this case.