color(red).
color(green).
color(blue).

adjacent(ibaraki,tochigi).
adjacent(ibaraki,saitama).
adjacent(ibaraki,chiba).
adjacent(tochigi,gunma).
adjacent(tochigi,saitama).
adjacent(gunma,saitama).
adjacent(saitama,tokyo).
adjacent(saitama,chiba).
adjacent(tokyo,chiba).
adjacent(tokyo,kanagawa).