$h_a[
    $.a[1]
    $.b[2]
    $.c[3]
]
$h_b[
    $.c[]
    $.a[]
]

1. ^json:string[^h_a.intersection[$h_b]]
2. ^json:string[^h_a.intersection[$h_b; $.order[arg] ]]
3. ^json:string[^h_a.intersection[$h_b; $.order[self] ]]