According to the gnoseological status, i.e. in relation to reality, answers can be true and false. The answer is regarded as true if the judgment expressed in it is correct, or adequately reflects reality. The answer is regarded as false if the judgment expressed in it is incorrect, or inadequately reflects a situation actually.
In the examples given above the knowledge needing addition is expressed in the following judgments: Somewhere the World World Cup took place; Someone invented phone; Once there was the last volcanic eruption Vesuvius.
This trick is under construction on uncertainty of the concept "heap". The sophist suggests to delete from a heap on one grain of sand, but the concept "heap" is not defined by their quantity, and by such qualitative characteristics as a form and relative size of object.