Conceal self [641]
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Usage:  USE 641 <flag>
Time:   three days

This skill allows a character to conceal itself from view.
When activiated, other characters will not see the unit in their
location reports, and will not see the unit come and go.

The unit must be alone in order to conceal itself.  It may not be
stacked with any other characters, or possess any followers, such
as peasants, soldiers, workers, etc.  It may also not be the first
character inside a sublocation, building or ship.  The owners of
these small locations are always visible.

Hiding takes three days to accomplish.  However, turning off
concealment takes zero time.

Use of the skill will set whether or not the unit is trying to
hide from view:

	use 641 1	# Hide from view, takes three days
	use 641 0	# Don't conceal self from view, zero days

Note that attempts to gain entrance to buildings or ships with
the MOVE order will subject to the unit to the ADMIT system.
A failure to gain entrance with MOVE will give the unit away to
the structure's owner.