What is the quality of the interval B♯ to F?
If you count from B to F, you get the generic interval 5th. So it must be some kind of 5th.
B ♮ to F♯ is a P5.
By lowering the upper note to F♮, it becomes a d5.
Then changing B to B♯, it becomes a P4, because the interval becomes smaller.
But B♯'s P4 is E♯, not F.
I can't find the answer anywhere. Software programs I tried don't even give me the option to check it, because if I try to check the possible intervals from B♯, it never shows an F♮.
Is this interval impossible?