reserve o,m for set;
reserve C for Cartesian_category;
reserve a,b,c,d,e,s for Object of C;
reserve C for Cocartesian_category;
reserve a,b,c,d,e,s for Object of C;

theorem Th55:
  Hom(EmptyMS C,a) <> {}
proof
  EmptyMS C is initial by Def26;
  hence thesis;
end;
