<p>A ''category'' is a deductive system in which the following equations hold, for all <math>f : A \to B,</math> <math>g : B \to C,</math> and <math>h : C \to D.</math></p> | <p>A ''category'' is a deductive system in which the following equations hold, for all <math>f : A \to B,</math> <math>g : B \to C,</math> and <math>h : C \to D.</math></p> |