I can think of a slightly more general solution to the problem of not being sure if A and B are different views on the same file or not, especially if you plan

I can think of a slightly more general solution to the problem of not being sure if A and B are different views on the same file or not, especially if you plan to hardlink one to the other: Hardlink A to a tempfile, hardlink the tempfile in place of both A and B, then remove the tempfile. This will give the right outcome regardless of whether A and B are secretly the same underlying file (assuming that they are on the same filesystem).