Hi. Am flummoxed by two of the mathematicians - and by two other clues in the NE corner:
10A Expression of surprise when meeting poet (8).
I have H*****O*
6A Crowd hanging round front of university (6).
Is there a mathematician called Preuss? I only have the final letter ('S' I think).
Barrio seemed a likely answer to 4D :"On-the-up Irish singer in Italian city district (6)" but I can't parse it - and it wouldn't fit with Preuss. Tho I have O as its last letter.
Hmmm.
Most of you have done this I guess as there are no other queries about that corner, so I look forward to hearing from you all!! Thank you!