`. as [$i, $j, $k] | ...`
`. as {a: $i, b: $j} | ...`
`. as [[[$i]], {a: $j}] | ...`
`foreach . as [$i, $j, $k] (...)`
`reduce . as {a: $i, b: $j} (...)`
`. as [$i, $j, $k] | ...`
`. as {a: $i, b: $j} | ...`
`. as [[[$i]], {a: $j}] | ...`
`foreach . as [$i, $j, $k] (...)`
`reduce . as {a: $i, b: $j} (...)`