For the following code:

trait List /* supertypeclass */
{
  type Next: List;
}
trait ListExtend: List
where
  <Self as List>::Next: ListExtend
{}

when you run cargo check, it returns 148 and says

    Checking tc_inheritance v0.1.0 (/home/rust/tc_inheritance)
error[E0277]: the trait bound `<<Self as List>::Next as List>::Next: ListExtend` is not satisfied
  --> src/lib.rs:15:25
   |
15 |   <Self as List>::Next: ListExtend {}
   |                         ^^^^^^^^^^ the trait `ListExtend` is not implemented for `<<Self as List>::Next as List>::Next`
   |
note: required by a bound in `ListExtend`
  --> src/lib.rs:15:25
   |
12 | pub trait ListExtend
   |           ---------- required by a bound in this trait
...
15 |   <Self as List>::Next: ListExtend {}
   |                         ^^^^^^^^^^ required by this bound in `ListExtend`
help: consider further restricting the associated type
   |
15 |   <Self as List>::Next: ListExtend, <<Self as List>::Next as List>::Next: ListExtend {}
   |                                   ++++++++++++++++++++++++++++++++++++++++++++++++++

For more information about this error, try `rustc --explain E0277`.
error: could not compile `tc_inheritance` (lib) due to 1 previous error

rustc somehow wants to show <Self as List>::Next: ListExtend, but isn't that a premise?

possibly related:

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