Fabio,

>My original is not clear.

Good, this subthread is just an issue of Italian to English translation and not one about how VFP evaluates null in a boolean expression.

>This is clear:
>

>.NULL. AND m.X <=== must return .F. if m.X is .F., then m.X must to be evaluated
>

yes that is now correct.

>or you understand where I have not written correctly and you correct to me,
>otherwise we write 1000 messages.

this should be added to your example:

.NULL. AND m.X <=== must return .null. if m.X is .T., then m.X must to be evaluated

an alternate English translation:

.NULL. AND m.X <=== will return .F. if m.X is .F., m.X will be evaluated
.NULL. AND m.X <=== will return .null. if m.X is .T., m.X will be evaluated
.NULL. AND m.X <=== will return .null. if m.X is .null., m.X will be evaluated