Advanced Engineering Mathematics by Erwin Kreyszig, 8th edition hardcover (John Wiley & Sons, 1999). Textblock appears intact with reading wear; cover corners and spine ends show bumped fraying and light board exposure. Pages photographed open; no loose sections visible. Broad reference covering differential equations, vector calculus, triple integrals, potential theory and problem sets — a standard college/engineering textbook for applied mathematics and mathematical physics.