let y1 = [1; 2; 3; 4; 5]
    let y2 = [10; 11; 12; 13; 14]
    let rec Comb = function
    | (a1::b1, a2::b2) -> a1::a2::Comb (b1, b2)
    | (a1::b1, [] ) -> a1::b1
    | ( [], a2::b2) -> a2::b2
    printfn "%A" (Comb (y1, y2))