I have two interrelated apparatus like a socket and a plug. I'd like to draft one independent claim for each one. Is it possible to draft 3rd independent claims included both apparatus? And if it is possible, after three independent claim, am i allowed to draft 4th independent claim for a system also comprises 3rd independent claim?
Note: Both of apparatus can be sold seperatly so I'd like to protect both. I believe, both of them novel but the second one may be not inventetive. So i don't want a second application for 2nd apparatus. Besides that their best use is provided together, because of that may be a good idea 3rd claim (if possible) to cover both if a problematic document appears. For same reason, if possible i'd like to draft 4th indepent claim for a system which 1st and second 2nd is actually is used in it.
Another note: It's EPO application and I know interrelated apparatus can be claimed in one application in a different independent claims. Please interpret my question taking this into consideration.