"Martin DeMello" <martindemello / yahoo.com> wrote in message
news:mV2G9.79479$ea.1364198 / news2.calgary.shaw.ca...
> Puzzle: There's a common occurrence of a doubly broken abstraction.
> Physically, the structure most resembles a stack; that is, inserting and
> removing are both trivial from the front end. However, people of one
> type go out of their way to insert objects in the back end, trying to
> convert the stack into a queue. And after that, the other class of
> people go out of their way to *remove* objects from the back end,
> turning the queue into a stack facing the other way, even though
> insertion and deletion from that end are both O(n). What am I talking
> about?

People shopping - fresh milk goes to the back of the queue.
Classes: customers and employees.

Mikkel