APA (7th ed.) Citation

Piper, H. B., & Schoenherr, J. (2007). Space Viking. Project Gutenberg.

Chicago Style (17th ed.) Citation

Piper, H. Beam, and John Schoenherr. Space Viking. Project Gutenberg, 2007.

MLA (9th ed.) Citation

Piper, H. Beam, and John Schoenherr. Space Viking. Project Gutenberg, 2007.

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