http://erlang.org/pipermail/erlang-questions/2017-September/093564.htmlIf A sends B the messages 1, 2 and 3 in that order, they will certainly
arrive in that order (assuming they arrive at all -- meaning that B is
available from the perspective of A). If C sends B the messages 4, 5, 6
in that order those will also certainly arrive in that order for B.
If A sends B and C the messages 1, 2 and 3, and as a reaction C starts
sending B the messages 4, 5, 6 -- we can never know what order of
interleaving these will have.