Vance's magic system IS D&D's magic system, to the point that the mechanic is still called Vancian casting by everybody who plays it. A wizard memorises a fixed set of spells, the words physically occupy the mind and are forgotten the instant they are spoken, so the morning's preparation decides what is possible all day and the spell is gone once used. Nothing in folklore or in earlier fantasy works that way. It is Vance's invention, taken whole. Gygax named The Dying Earth in Appendix N, the reading list printed in the 1979 Dungeon Master's Guide, and said so repeatedly afterwards. Individual Vance spells survive by name in the rules, including prismatic spray, from his Excellent Prismatic Spray. The eccentric, scheming, self-interested magicians of the Dying Earth stories came across with the mechanic. Vance supplied the D&D wizard as a character type, not only as a spell list.