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	It has been routinely observed, that when simulating a robot,
one must have two world models: one world model external to the robot
and the other world model internal to the robot.

	"The design,  implementation, and use  of the  robot hardware
presents  some   difficult,  and  often  expensive,  engineering  and
maintenance problems. If  one is to  work in  this area solving  such
problems it is a  necessary  prelude   but,  more  often   than  not,
unrewarding  because the activity  does not address  the questions of
A.I. reseach  that motivate  the project. Why,  then, build  devices?
Why not simulate  them and their environment? In  fact, the SRI group
has done  good work  in simulating  a  version of  their robot  in  a
simplified environment. The  answer given is  as follows. It  is felt
by  the  SRI  group  that  the  most  unsatisfactory  part  of  their
simulation effort was  the simulation of  the environment. Yet,  they
say that  90% of  the effort  of the simulation  team went  into this
part  of  the  simulation. It  turned  out to  be  very  difficult to
reproduce in an internal representation for a  computer the necessary
richness of environment that  would give rise to interesting behavior
by the highly  adaptive robt.  It is easier  and cheaper  to build  a
hardware robot  to extract what  information it  needs from the  real
world  than to organize  and store a  useful model.  Crudely put, the
SRI group's argument  is that the most  economic and efficient  store
of information about the real world is the real world itself."

					- E. A. Fiegenbaum [ref. X].

	The real world of  course represents itself, but it  is not a
good  memory  of   itself  because  there  is  no  simple  addressing
mechanism. A machine can not  easily (i.e.  directly) read the  world
states that  are relevant  to its given  task. Conclusions  about the
state  of the  world are  reached by  incredible chains  of reasoning
based (in the  case of vision)  on how the  world scatters a  certain
band  of  incoherent  electromagnetic  radiation. In  particular,  it
appears  to   me  that   perception  itself   requires  an   internal
environmental simulation almost  exactly like the  external simulator
Fiegenbaum mentions.