fn prod(list: Vec<Vec<u32>>, next: &Vec<u32>) -> Vec<Vec<u32>> {
    let mut result = vec![vec![0; 0]; 0];
    for item in list {
        for subitem in next {
            let mut result_item = item.clone();
            result_item.push(*subitem);
            result.push(result_item);
        }
    }
    result
}

fn main() {
    let list = vec![vec![1, 2], vec![3, 4], vec![5, 6, 7]];
    let mut result = vec![vec![0; 0]];
    for item in list {
        result = prod(result, &item);
    }
    println!("Result is {:?}", result);
}