category with pullbacks and products has equalizers. Weak pullbacks A weak pullback of a cospan is a cone over the cospan that is only weakly universal, that is, the mediating morphism above is not required to be unique. See also Pullbacks in differential geometry Equijoin in relational algebra Fiber product of schemes Notes References Adámek, Jiří, Herrlich, Horst, & Strecker, George E.; (1990). Abstract and Concrete Categories (4.2MB PDF). Originally publ. John Wiley & Sons. . (now free on-line edition). Cohn, Paul M.; Universal Algebra (1981), D. Reidel Publishing, Holland, (Originally published in 1965, by Harper & Row). External links Interactive web page which generates examples of pullbacks in the category of finite sets. Written by Jocelyn Paine. Limits (category theory)