No one else has yet been found to have psychic powers. It is possible to determine whether Selena has psychic powers. We will not be able to determine whether it is possible to have psychic powers unless we find out whether Selena's claim is true. If it is possible to have psychic powers, then Selena has them.
Selena claims to have psychic powers. So if we find out whether Selena' s claim is true, we will thereby determine whether it is possible to have psychic powers.
The conclusion drawn above follows logically if which one of the following is assumed?