@phil: But if two are inactive its four days. And that already is very annoying. I can't wait four days 
About the seven lines limit... I'm not sure if I can manage to write less every time
Another possibility would be that if you write a very long part just write half of it, post it and edit it afterwards, maybe with a note "will be edited soon". Or you please the ninja to change his post a bit.
Only problem is that you then have to think : Should I wait with writing? Or should I post and hope that he isn't writing something that doesn't fit. Again a PM would be a possibility. But thats getting so complex...
So to put it short and simple, idk.

About the seven lines limit... I'm not sure if I can manage to write less every time

Another possibility would be that if you write a very long part just write half of it, post it and edit it afterwards, maybe with a note "will be edited soon". Or you please the ninja to change his post a bit.
Only problem is that you then have to think : Should I wait with writing? Or should I post and hope that he isn't writing something that doesn't fit. Again a PM would be a possibility. But thats getting so complex...
So to put it short and simple, idk.

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