found: Work cat.: Hodge, D.B. The calculation of the eigenvalues and eigenfunctions of Mathieu's equation, 1972.

found: International dictionary of applied mathematics, 1960:p. 571 ("Mathieu equation - a differential equation resulting from the separation, in elliptical cylindrical coordinates, of partial differential equations like Laplace's or the wave equation. It also occurs in the quantum mechanical problem of a molecule with restricted internal rotation")

found: Eric Weisstein's World of mathematics, via WWW, Oct. 8. 2002("Mathieu differential equation ... The equation arises in separation of variables of the Helmholtz differential equation in elliptic cylindrical coordinates")

found: Encyclopedic dictionary of mathematics, 1987:v. 2, p. 990 (under heading, Mathieu functions, "Mathieu differential equation" - An equation derived from a 2-dimensional Helmholtz equation when the latter is separated in elliptic coordinates [cataloger's paraphrase])

found: Google search, Oct. 8, 2002 ("Mathieu equation" - 1080 hits: "Mathieu's equation" - 260 hits; "Mathieu differential equation" - 102 hits; "Mathieu's differential equation" - 72 hits)