1 import CW9a._

     2 

     3 assert(is_legal(8, Nil, (3, 4)) == true)

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

     5 assert(is_legal(2, Nil, (0, 0)) == true)

     6 

     7 

     8 

     9