
theorem Th5:
  for A,B being category st A,B are_isomorphic holds A,B are_equivalent
proof
  let A,B be category;
  assume A,B are_isomorphic;
  then consider F being Functor of A,B such that
A1: F is bijective covariant;
  reconsider F as covariant Functor of A,B by A1;
  consider G being Functor of B,A such that
A2: G = F" and
A3: G is bijective covariant by A1,FUNCTOR0:48;
  reconsider G as covariant Functor of B,A by A3;
  take F, G;
  thus thesis by A1,A2,FUNCTOR1:18,19;
end;
