In the desert, there is a cave containing an inexhaustible spring. An
ancient gate exists which is impregnable, and can be latched from the
inside. This cave has been unknown for 5,000 years.

Subject A comes on the cave and enters in, drinking water from the
spring. Some time later, subject B approaches, and subject A locks the
gate. There is a reasonable probability that B will die of thirst, but
as with all probabilities we can't be certain.

Does subject A have a RIGHT to lock the gate?