removed unnecessary \mathrm
Relations for general categories
Predicate Implications for general categories
No wrong sequents in file to be parsed
IsIdentity -> IsOne
UniversalMorphismIntoDirectProduct

now with diagram as argument
Created new files

for the hierarchy of categories used in homological algebra.
IsMonomorphism and IsEpimorphism

in Ab-categories
Deleted superfluous theorem
Axiom for abelian categories
List -> ListObj, ListMor
Fixed precompose in relations.