Is this sentence grammatically correct:
Non necessarily convex nor simply connected
Is probably a typo, and should be
Other than that, the sentence is fine, especially if you add a comma before "nor". You can use "nor" without "neither" to connect two negative sentences.
I haven't travelled to Canada, nor am I planning to.
Nor is also used as a short answer to agree with a negative statement
-- I don't smoke.
--Nor (do) I. (a little too formal, I guess)