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C00002 00002	travel[e88,jmc]		Travel with obstacles, common sense
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travel[e88,jmc]		Travel with obstacles, common sense

	Travel with obstacles should be a good common sense domain.

Basics:
	travel by airplane, car, train, bus, walking
	We include information about what will be known
in the future.  Thus validating a plan for airplane travel
may require that we reason that we will be able to find
the gate of the outgoing flight from an intermediate stop.

The preliminary version will validate plans on the basis of
initial information.  Later we will include the part that
deals with problems that arise in the course of the journey.

Obstacles:
	flight cancelled, need wheelchair, need visa, need money,
need hotel reservation, 

Facts about visas to be formalized:

Some countries require a visa from citizens of certain other countries
to enter.  The visa is obtained from a consulate of the country to
be entered.  Travel agents know which countries require visas.
Depending on what one intends to do in the country, different visas
with different justifications may be required.
Can visas be handled entirely by Horn clauses?  Is negation as failure
sufficient to determine that a visa cannot be obtained?