I want to express that fact A and fact B generate/produce/yield fact C.
However, I want to state that as "A, (together with B), [give/gives] C."
What should I use? Give or gives.
Interesting question. To my ear, your second sentence should use the the third person singular conjugation(i.e. 'gives').
A grammatical justification would be that our subject is still only A, which by itself necessarily requires a third person singular conjugation. Your addition of "together with B" modifies A but does not change the subject, therefore, we must still use the conjugation 'gives'. Hope this helps!