If A enters Whiteacre believing it to be Blackacre, does he commit trespass?

A is indeed liable to the possessor of Whiteacre because trespass to land is determined by the act of entering or remaining on the land of another without permission. The intent or belief regarding the ownership of the property does not absolve a person from liability if they physically enter the land.

In this situation, A's mistaken belief that he is on Blackacre rather than Whiteacre does not negate the fact that he entered someone else's property without permission. The critical element in establishing liability for trespass is the unauthorized entry itself, irrespective of A's subjective belief about the land's ownership.

The other options highlight different perspectives on liability, such as permission and misrepresentation, but do not apply since A's entry remains unauthorized regardless of what he believed.