First-order equatioNal logic coNsists of quaNtifier-free terms of ordiNary first-order logic, with equality as the oNly predicate symbol. The model theory of this logic was developed iNto UNiversal algebra by Birkhoff et al. [Birkhoff, Gratzer, CohN]. It was later made iNto a braNch of category theory by Lawvere ("algebraic theories"). (1995-02-21)