I am trying to learn Vue3 + Typescript (I so far wrote Vue2 apps with plain JS). I am trying to define a reactive variable in `setup()` :

```
setup() {
    // a single note
    interface Note {
      id: string
      creationDate: string
      text: string
      tags: string[]
      deleted: boolean
    }
    // all the notes in the app
    let allNotes: ref(Note[])  // ← this is not correct
    let allnotes: Note[]  // ← this is correct but not reactive

    (...)
  }

```

What is the correct syntax for creating a reactive Array of `Note`?