- (i) the class of morphisms has to be closed under composition:
- where f:C1→C2 and g:C2→C3, g ∘ f is also a
- morphism of the category, which maps C1→C3.
- (ii) composition of morphisms has to be associative
+ (i) the class of morphisms has to be closed under composition:
+ where f:C1→C2 and g:C2→C3, g ∘ f is also a
+ morphism of the category, which maps C1→C3.
+
+ (ii) composition of morphisms has to be associative
+
- morphism 1<sub>E</sub>, which is such that for every morphism
- f:C1→C2: 1<sub>C2</sub> ∘ f = f = f ∘ 1<sub>C1</sub>
+ morphism 1<sub>E</sub>, which is such that for every morphism f:C1→C2:
+ 1<sub>C2</sub> ∘ f = f = f ∘ 1<sub>C1</sub>