1 

     2 assert(CW7a.is_legal(8, Nil)(3, 4) == true)

     3 assert(CW7a.is_legal(8, List((4, 1), (1, 0)))(4, 1) == false)

     4 assert(CW7a.is_legal(2, Nil)(0, 0) == true)

     5