func (p *PubSub) seenMessage(id string) bool {
	return p.seenMessages.Has(id)
}
func (p *PubSub) seenMessage(id string) bool {
	return p.seenMessages.Has(id)
}
func ( p * PubSub ) seenMessage ( id string ) bool { return p . seenMessages . Has ( id ) }
// seenMessage returns whether we already saw this message before
seenMessage returns whether we already saw this message before