Please read Alexey Sklyarenko's annotations on Pale Fire, Ada and other Nabokov works here.
Describing the suicide of poor mad Aqua (the twin sister of Van's, Ada's and Lucette's mother Marina), Van Veen (the narrator and main character in VN's novel Ada, 1969) mentions the Dr Froit of Signy-Mondieu-Mondieu in the Ardennes and a Dr Sig Heiler:
In VN’s novel Transparent Things (1972) the spectral narrators discuss the history of a pencil:
In VN’s play Sobytie (“The Event,” 1938) the action takes place on the fiftieth birthday of Antonina Pavlovna Opayashin (the lady writer). At her birthday party Antonina Pavlovna says that in India there is a belief that only great people die on their birthday:
Антонина Павловна. За себя я спокойна. В Индии есть поверье, что только великие люди умирают в день своего рождения. Закон целых чисел.
Любовь. Такого поверья нет, мамочка. (Act Two)
After his father's sudden death Hugh Person (the main character in VN's novel Transparent Things, 1972) moves to Geneva, has homard à l'américaine for dinner and goes to find his first whore:
In VN’s novel Transparent Things (1972) the spectral narrators discuss the history of a pencil:
According to Mr. R. (the writer in VN’s novel Transparent Things, 1972), all he can offer his publisher is not Tralala but the first and dullest tome of his Tralatitions:
In VN's play Izobretenie Val'sa ("The Waltz Invention," 1938) Salvator Waltz wants to rule the world from Palmora (a distant island, Palmera in the English version) and exclaims: “Na Palmoru, skorey na Palmoru!” (“To Palmera, to Palmera as soon as possible!”):
In VN’s novel Transparent Things (1972) Hugh Person kills his wife Armande in his sleep, dreaming of Giulia Romeo (a prostitute whom he had picked up on his first trip abroad):
According to Mr. R. (the writer in VN’s novel Transparent Things, 1972), the name of his secretary, Mr. Tamworth, is pronounced like that of the English breed of black-blotched swine:
Reading the galleys of Mr. R.’s Tralatitions, Hugh Person (the main character in VN’s novel Transparent Things, 1972) ponders the name of an incidental character "Adam von Librikov:"