Concerning Linear Substitutions of Finite Period with Rational Coefficients
Arthur Ranum · Transactions of the American Mathematical Society · 1908
f In this paper I shall confine my attention to matrices whose determinants do not vanish and therefore define the period of a matrix and the identity matrix in the usual way ; in another paper soon to be published elsewhere I shall consider groups of matrices whose determinantsvanish, and arrive at a more general definition of the concepts period and identity matrix.t Modulfunktionen, vol. 1, p. 182.183