I tried submitting an alias suggestiong for one_leg_up and raised_leg but the site said both of them are already aliased, despite neither of their wiki pages saying anything. I searched and saw that I was not the first one to suggest this. Is it a bug?

While I'm at it, I think on_one_leg could imply them.

They both have pending aliases/implications. Pending aliases or implications count for making aliases/implications, meaning you can’t make aliases if there are any pending to or from.

https://e621.net/forum/show/215049 someone already suggested one to the other.

OneMoreAnonymous said:
While I'm at it, I think on_one_leg could imply them.

What if the character on one leg has more than two legs? Or the leg not touching the ground isn't raised enough to be considered raised? Or isn't raised at all and simply has no ground beneath it?

I feel like a distinction can be made between a leg raised high and a leg lifted off the ground only slightly. So

post #1303059 vs post #1378913

I don't know if maintaining such a distinction would be useful, but it's there.

legs_up currently uses "legs above the waist and/or stretched up into the air" for criteria, which would be fine boundaries here.