逻辑编程着色问题

color(red).
color(green).
color(yellow).
color(blue).%测试三色是不够的
colorUP(AB,AC,AD,BA,BC,BD,DA,DB,DC,EA,EB,EC,ED):-
    color(AB),color(AC),color(AD),
    color(BA),color(BC),color(BD),
    color(DA),color(DB),color(DC),
    color(EA),color(EB),color(EC),color(ED),%各通行方向颜色
    AB\=BC, AB\=BD, AB\=DA, AB\=EA,%AB\=BC，A->B跟B->C冲突
    AC\=BD, AC\=DA, AC\=DB, AC\=EB, AC\=EA,
    AD\=EA, AD\=EB, AD\=EC,
    BC\=DB, BC\=EB,
    BD\=DA, BD\=EB, BD\=EC,
    DA\=EB, DA\=EC,
    DB\=EC. 

SWISH的运行结果：
AB = AC, AC = AD, AD = BA, BA = DC, DC = ED, ED = red,
BC = BD, BD = EA, EA = green,
DA = DB, DB = yellow,
EB = EC, EC = blue