Strohmeier, Alfred; Genillard, Christian; Weber, Mats (1990-08-01). "Ordering of characters and strings". ACM SIGAda Ada Letters (dalam bahasa Inggris) (7): 84. doi:10.1145/101120.101136.Parameter |s2cid= yang tidak diketahui akan diabaikan (bantuan)
Macpherson, H. Dugald (2011), "A survey of homogeneous structures", Discrete Mathematics, 311 (15): 1599–1634, doi:10.1016/j.disc.2011.01.024
Ganapathy, Jayanthi (1992). "Maximal Elements and Upper Bounds in Posets". Pi Mu Epsilon Journal. 9 (7): 462–464. ISSN0031-952X. JSTOR24340068.
loc.gov
lccn.loc.gov
Brian A. Davey and Hilary Ann Priestley (1990). Introduction to Lattices and Order. Cambridge Mathematical Textbooks. Cambridge University Press. ISBN0-521-36766-2. LCCN89009753. Di hlm. 100
worldcat.org
Ganapathy, Jayanthi (1992). "Maximal Elements and Upper Bounds in Posets". Pi Mu Epsilon Journal. 9 (7): 462–464. ISSN0031-952X. JSTOR24340068.