Negative Research prereqs
Preventing research.
I looked and couldn't find a way to prevent a research option based on if another research option was completed. For example I want to have 3 final tier research options. Shields, Armor and Weapons. They are fairly substantial upgrades and are rather expensive, but I want only one to be available. So if a player researches the final tier option for shields then the other two final tier options become unavailable. Thanks in advance.