for x1, x2, x3, x4, x5, x6 being set st x1,x2,x3 are_mutually_distinct & x4,x5,x6 are_mutually_distinct & {x1,x2,x3} misses {x4,x5,x6} holds
x1,x2,x3,x4,x5,x6 are_mutually_distinct