Information Processing

This is a joke some maths-professor of Oxford told, and his colleagues were
laughing their heads off:

In a Scottish village the rumour runs that one of them will travel to London.
Mr. Dunn appears on the doorstep of the future traveller and asks him to do
him a favour:
“Listen, my son Neal lives in London, and we have not had a message from him
for two years.
All I have is his address, London WC3.”
“I sure will find him,” says the traveller and tucks away the scrap of paper
Mr. Dunn holds out to him.
When the traveller arrives at the airport of London he sees a sign “WC”,
says “aha”,
enters,
counts the cabins: one two three,
knocks on door number three,
and asks: “Are you Nealy Dunn?”
“Yes,” is the answer from the inside
“but I ran out of paper!”
“Aw, that is a bad excuse for not writing to your parents for such a long
time!!!!”