APA (7th ed.) Citation

Hamilton, E. (2010). The Door into Infinity. Project Gutenberg.

Chicago Style (17th ed.) Citation

Hamilton, Edmond. The Door into Infinity. Project Gutenberg, 2010.

MLA (9th ed.) Citation

Hamilton, Edmond. The Door into Infinity. Project Gutenberg, 2010.

Warning: These citations may not always be 100% accurate.