Axiom 1: no matter what have been written is right or wrong
Axiom 2： It is not necessary to read and write back
Axiom 3: It is preferable to think different technical details in collaboration
Axiom 4: A joint authorship is always superior than single authorship even if there is no contribution from one or the other to avoid quarrels.
From extract from Henrik Bohr in the foreword written by BB