Hello, you don't have to pick an invertible F(), the way the L and R sides are combined together leads automatically to the network to be invertible. This is th

Hello, you don't have to pick an invertible F(), the way the L and R sides are combined together leads automatically to the network to be invertible. This is the magic of Feistel networks, that F() can be as complex as you want and can be not invertible at all.