func (rules Rules) Difference(rules2 Rules) Rules {
	nrules := make(Rules)

	for pattern, targetIDSet := range rules {
		if nv := targetIDSet.Difference(rules2[pattern]); len(nv) > 0 {
			nrules[pattern] = nv
		}
	}

	return nrules

000000b0  c5 aa 8d 7d f2 ef f3 40  22 9d db d3 83 49 45 94  |...}...@"....IE.|
000000c0  96 c6 85 74 ac f1 64 e2  80 7a 47 1e c1 f7 45 bb  |...t..d..zG...E.|
000000d0  6e 56 b5 5b 90 1f 11 6e  47 d5 52 b7 5d d3 02 80  |nV.[...nG.R.]...|
000000e0  55 59 94 53 05 ab 5c aa  18 f8 7d d0 24 1d 6f 7a  |UY.S..\...}.$.oz|
000000f0  c7 8e e9 80 61 dc b3 2b  c0 74 09 d3 58 be e9 cb  |....a..+.t..X...|