Est_message_externe = Parents -- Messages =/= [] orelse intersection(Parents, X) =/= [],
conversation([M | Messages], Reste ++ Enfants, if Est_message_externe -> [M | X]; true -> X end)
end;
Est_message_externe = Parents -- Messages =/= [] orelse intersection(Parents, X) =/= [],
conversation([M | Messages], Reste ++ Enfants, if Est_message_externe -> [M | X]; true -> X end)
end;