Homomorphisms of unary algebras and of their expansions
William A. Lampe, Jiří Sichler, Věra Trnková · Colloquium Mathematicum · 1993
According to [4], a functor Ψ is regularly faithful iff Ψ is a composite Ψ = Ψ 1 • Ψ 0 of a full embedding (that is, a full and faithful functor) Ψ 1 and an equalizer Ψ 0 in the category of all small categories.We say that a variety is universal if it contains an isomorphic copy of any small category as a full subcategory.