1. Black, Charles. "Folding step for vehicles." U.S. Patent 903,352, issued November 10, 1908.
2. Demski, Richard F. FOLDING STEP SYSTEM FOR WEHICLES. US Patent USOO5584493A, filed February 3, 1995, and issued December 17, 1996.
3. Lee, Byung-tae. "Folding staircase." U.S. Patent 5,941,342, issued August 24, 1999.
4. Structure synthesis and statics analysis of a foldable stair
5. Craig, Roy R. Mechanics of Materials. Hoboken, NJ: Wiley, 2011.