Complex output layer regularization implementation


Hi guys. I’m building a NN model using keras, and I wish to impose a constraint on it that doesn’t (directly) have to do with the weights. Would be very grateful for some help / points me towards some relevant keywords to look up. The constraint I wish to impose is a bit complex, but it can be simplified in the following manner:
I wish to impose a constraint on the output of certain inputs of the net. For the sake of simplicity, let’s say the constraint looks like NN(3)+NN(4) < 10, where NN is the neural net, which can be seen as a function.
How can I impose such a constraint?

Thank you very much in advance for any help on the subject!