How to remove/mutate things (shells, aliases) in nushell

I'm using shells and enter to manage a "dirstack". I want to "popd" to remove dirs I've added.

I also have some aliases that I no longer want in my session. How do I delete the aliases?

I've tried things like drop but if the dirs and aliases are possibly immutable, how do I change them (without starting a new session)? Feels like there should be commands like leave (or unenter vs enter) and unalias (vs alias).

You can "Hide definitions in the current scope" with the hide command.

alias ll = ls -al
hide ll
ll

Error: nu::shell::external_command

  × External command failed
   ╭─[entry #49:1:1]
 1 │ ll
   · ─┬
   ·  ╰── did you mean 'all'?
   ╰────
  help: No such file or directory (os error 2)

As for the pushd/popd equivalency (see the docs), you can enter a new shell with enter, and exit it with dexit. You can inspect the table with shells or g, and activate the next or previous directory with n and p.