example.cel

state.map(e, has(e.other) && e.other != '',
	has(e.num) && size(e.num) != 0 && has(e.let) && size(e.let) != 0 ?
		// Handle Cartesian product.
		e.num.map(v1,
			e.let.map(v2,
				e.with({
					"@triggered": now,   // As a value, the start time.
					"@timestamp": now(), // As a function, the time the action happened.
					"original": e.encode_json(),
					"numlet": e.num+e.let,
					"num": v1,
					"let": v2,
				})
		))
	:
		// Handle cases where there is only one of num or let and so
		// the Cartesian product would be empty: S × Ø, S = num or let.
		//
		// This expression is nested to agree with the Cartesian
		// product (an alternative is to flatten that for each e).
		[[e.with({
			"@triggered": now,   // As a value, the start time.
			"@timestamp": now(), // As a function, the time the action happened.
			"original": e.encode_json(),
		})]] 
).flatten().drop_empty().as(res,
	{
		// Get cursor summary.
		"events": res,
		"cursor": res.collate('@timestamp').as(t, {"timestamps":{
			"first": t.min(),
			"last": t.max(),
			"list": t,
		}}),
	}
)