J does look vaguely like APL's ⍳

but yeah there's a ton of stuff that just got stuck on something unrelated because those characters were already in the code page and unused I guess

Ẹ's mnemonic could be "exists"

I guess Ụ is "grade up" but why is it called grade up to begin with? and the distinction between grade up and grade down is ascending versus descending sort, but Jelly doesn't have a descending version

and yeah I can't see any logic at all to the other ones lmao