The coach of a national football team found that the best cooperation characteristics of players U, V, W, X, Y and Z in the process of training are: (1) V and X cannot both be on the field or not on the field  (2) only U is not on the field, V is not on the field  (3) if W is on the field, X should also be on the field
V and W are on the court
 (4) if Y and Z are on the field, W must also be on the field