For space groups, see

http://cci.lbl.gov/sginfo/hall_symbols.html.

Hermann-Mauguin are not unique, the Hall symbol is.

C2/c is space group 15. You have the following flavors:

15:b1 C 1 2/c 1 -C 2yc

15:b2 A 1 2/n 1 -A 2yac

15:b3 I 1 2/a 1 -I 2ya

15:-b1 A 1 2/a 1 -A 2ya

15:-b2 C 1 2/n 1 -C 2ybc

15:-b3 I 1 2/c 1 -I 2yc

15:c1 A 1 1 2/a -A 2a

15:c2 B 1 1 2/n -B 2bc

15:c3 I 1 1 2/b -I 2b

15:-c1 B 1 1 2/b -B 2b

15:-c2 A 1 1 2/n -A 2ac

15:-c3 I 1 1 2/a -I 2a

15:a1 B 2/b 1 1 -B 2xb

15:a2 C 2/n 1 1 -C 2xbc

15:a3 I 2/c 1 1 -I 2xc

15:-a1 C 2/c 1 1 -C 2xc <-----

15:-a2 B 2/n 1 1 -B 2xbc

15:-a3 I 2/b 1 1 -I 2xb