The impact of append and element modifications on the original slice

Let's consider an example that shows how changing slice elements and applying the append function inside a passed function affect the slice itself. Determine what output will be obtained at each stage of program execution.

func main() {
    mutate := func(a []int) {
        a[0] = 0
        a = append(a, 1)          // ?
        fmt.Println(a)            // ?
    }

    a := []int{1, 2, 3, 4}
    mutate(a)
    fmt.Println(a)                // ?
}