Should there be only one context function literal syntax?

[bishabosha]

Minimized example

val m = (x: Int) ?=> x       // query style, mirrors type
val n = (using x: Int) ?=> x // mixing styles
val o = (using x: Int) => x  // used by the MOOC

Output

they all compile

Expectation

Only one of these should be accepted I assume. Looking at the syntax these are all legitimate, but the docs uses the third kind

[OlivierBlanvillain]

Yes! I vote for the last one.

[odersky]

Yes, it was an oversight that the old syntax was not removed. I'll get to it.