A morphism is a map between two objects in an abstract category. 1. A general morphism is called a homomorphism, 2. A morphism f:Y->X in a category is a monomorphism if, for any two morphisms u, v:Z->Y, f u = f v implies that u = v, 3. A morphism f:Y->X in a category is an epimorphism if, for any two morphisms u, v:X->Z, u f = v f implies u = v, 4. A bijective morphism is called an isomorphism (if there is an isomorphism between two objects, then we say they are isomorphic), 5.