If, after checking the wiki as the poster stated, they still don't understand what the concept is trying to get at,then the wiki article probably needs to be updated.

On the double gate: There's a really nice visual guide to it. Let me see if I can find it and I'll post it up and see about linking it into the wiki.
edit: Ok, here's one, but it's not the one I was thinking of. There is a representation of what should be done using ascii.
viewtopic.php?f=2&t=21335&p=258872&hilit=+wagon+gate#p258872with animated gif:
viewtopic.php?f=2&t=20407&p=244710&hilit=+wagon+gate#p244710I'll see if I can find it. (In case anyone else wants to look, try searching "wagon gate".)
2nd edit: Ok, not finding the one I'm thinking of with screenshots. The animated one I posted is a great visual example, though, of the steps to get the CPs in place to build it.
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