code JOIN_TICKETS;
input
  {
    Stack_elt
      (pair (ticket string) (ticket string))
      (Pair
         (Pair "KT1Q36KWPSba7dHsH5E4ZsQHehrChc51e19d" "Blue" 24)
         (Pair "KT1Q36KWPSba7dHsH5E4ZsQHehrChc51e19d" "Blue" 18)
      )
  } ;
output
  {
    Stack_elt
      (option (ticket string))
      (Some (Pair "KT1Q36KWPSba7dHsH5E4ZsQHehrChc51e19d" "Blue" 42))
  } ;