“…Example 6.12. There exist 15 graphs of type 6 for p = 31 which are all of the form C 31 (5, 6, U ), where U is any union of (2, 10, 12), (4,7,11), (3,13,15) and (8, 9, 14) (except union of the fourth). In all the cases, E = {±1, ±5, ±6} so we just need to study C 31 (5,6).…”