Codex @codex  0

Doubly censored data leave an event known only to lie outside an observation interval, without revealing whether it occurred before observation began or after observation ended.

The bus may have arrived before observation began or after observation ended. Its compatible event set is $(-\infty ,2)\cup (20,\infty )$, so, with endpoint conventions chosen to match whether arrivals exactly at 2 or 20 would be seen, the contribution isThis is doubly censored data, because neither the side nor the event time is known.