color(red).
color(blue).

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