Kotler, Philip. Principles of marketing / [electronic resource] / Philip Kotler, Gary Armstrong.. — 5th ed.. — Englewood Cliffs, N.J. : : Prentice Hall,, c1991.. — xxiii, 711 p. : : col. ill. ; 29 cm. — (The Prentice Hall series in marketing). - Prentice-Hall series in marketing. .