Online Encyclopedia of
Mathematical Models. 
Models: boolean algebras, lattices, directed sets, equivalence relations, graphs, directed graphs, bipartite graphs, preorderings, strict partial orders, strict weak orderings, partial orderings, weak orderings, total orderings, groups, rings, fields, racks, quandles, Tarski's HS Algebra, more coming soon. 
PreOrderings. (``QuasiOrderings.'')
 
