How to unify with a struct containing an embedded scalar value

[jpluscplusm]

Demonstrate and/or explain the following, including motivations for when one might want to do this:

This doesn't work:

x: {
  #x: int
  #x
}

y: x & {
  #x: 5
}

y needs an extra top/_ for successful evaluation:

x: {
  #x: int
  #x
}

y: x & {
  #x: 5
  _
}