Phenomena that are mutually exclusive must be different and have no common locus. Non-existents such as the horns of a rabbit cannot be mutually exclusive with anything because they are not phenomena. On this page when the fields are submitted, the diagram and the statement “There is nothing that is both A and B” reveal the meaning of no common locus. As Perdue points out, a common locus is not something that exists half-way between the two and is neither. Rather, it is something which is both.
There is nothing that is both [ ] and [ ].