Recently I played Cities & Knights with two friends and we came in a situation for which we didn't knew a solution. I couldn't find it anywhere in an online discussion as well.
Player A wants to play the defector card on player B. Player B has two level two knights. Player A has one level one knight and one level two knight and no more space for new knights. Is player A allowed to voluntarily remove his level one knight and then play the defector card so he ends up with two two level knights? Or are you not allowed to take away a knight voluntarily?