Very grateful for all help with these three clues please.
7ac: "Point maintained by Chebyshev? (4,2,5)." I have E-S-,B-,S-U-H.
55ac: "Irish nationalist of note returned by London police (5)." I have --M-T.
50dn: "Rising crime - that periodically obsessed tea drinker (5)." I have T---C.