 It is important to recognize that Bohr discovered and wrote about all these correspondence relations; the disagreement among Bohr scholars is simply which (if any) of these correspondence relations Bohr meant to designate as the correspondence principle. Some scholars have even gone so far as to doubt whether Bohr ever had a well-defined and unvarying definition of the correspondence principle at all. These and other interpretations of the correspondence principle are elaborated in more detail in Section 5 below.