Acknowledging Sources

An author can acknowledge his literary sources in an introduction/author's note/afterword etc or in the text. Poul Anderson's Author's Note to The Psychotechnic League informs his readers that he modeled his Psychotechnic History on Robert Heinlein's Future History. Anderson's Introduction to Operation Chaos tells us that its idea of magic as technology derives from Heinlein's "Magic, Inc."

However, let us find some acknowledgments within the texts. In Heinlein's Future History, the title character of Volume I, The Man Who Sold The Moon, says:

"'I read Verne, and Wells, and Smith...'"
-Robert Heinlein, "Requiem" IN Heinlein, The Man Who Sold The Moon (London, 1963), pp. 222-238 AT p. 226.

So, straight off, we have Anderson acknowledging Heinlein who in turn acknowledges Verne, Wells and Smith. Elsewhere in The Man Who Sold The Moon, we read:

"In 1900 Herbert George Wells pointed out that the saturation point in the size of a city might be mathematically predicted in terms of its transportation facilities."
"The Roads Must Roll," pp. 49-85 AT p. 56.

Anderson acknowledges Wells without naming him in There Will Be Time (see here) and maybe even less directly in "Time Patrol" when Manse Everard time travels to the year in which The Time Machine was published. In Operation Luna, Anderson's sequel to Operation Chaos, the narrator reads novels by Lyle Monroe, which was a pen-name of Heinlein.

Heinlein's The Door Into Summer, about both suspended animation and time travel, acknowledges Mark Twain by mentioning Connecticut in its opening sentence and Wells by informing us that the insurance companies give away free copies of The Sleeper Awakes.

SM Stirling acknowledges:

Twain when Hong nicknames Walker "'Mr. Montana Maniac at King Agamemnon's Court.'" (Against The Tide Of Years, p. 238);

ERB in The Sky People - and again in Against The Tide... when Alston, hearing "...a weird yell...," thinks, "Maybe it's Tarzan...," (p. 270), then goes on to mention Burroughs by name;

Anderson and other fsf writers in Conquistador.

Thus:

Heinlein acknowledges Verne, Wells, Smith and Twain;
Anderson acknowledges Wells and Heinlein;
Stirling acknowledges Twain, Burroughs and Anderson.