Read this: At the time structures such as Lie algebras and hyperbolic quaternions drew attention to the need to expand algebraic structures beyond the associatively multiplicative class. In a review Alexander Macfarlane wrote: "The main idea of the work is not unification of the several methods, nor generalization of ordinary algebra so as to include them, but rather the comparative study of their several structures." In a separate review, G. B. Mathews wrote, "It possesses a unity of design which is really remarkable, considering the variety of its themes."

Reviewer Alexander Macfarlane believed that the main idea of the work is a comparative study of what?
What is the answer? (If it cannot be answered, return "unanswerable")
several structures