Online Tickets.

When you buy your ticket online they send you an email. That email is your ticket. It's 4 pages long as a printed item. They advise you to bring your ticket on your phone or as a printed item.

I never bring my ticket on my mobile phone as it often runs out of electricity. I always print my tickets out.

But being 4 pages long, think about it, all that paper and printing ink, hardly an example of good design. So why not a simple one page PDF file?