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C00002 00002	%tower[s90,jmc]		Epistemology of towers in the blocks world
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%tower[s90,jmc]		Epistemology of towers in the blocks world

	The object of formalizing towers in the blocks world is
to express the intuition that if an object is to be built to
satisfy a requirement, we first design it and then plan its
construction.  Realizing this object in the blocks world requires
several reifications beyond the blocks.  Here are some of them
(maybe enough).

1. towers: A tower consists of a collection of blocks arranged in
a particular way.  In the simple blocks world, a tower may be
represented by a list of its blocks, e.g. (A B F D) perhaps top
down, i.e. A is on top of B which is on top of F, etc.

2. designs: A design is like a tower except that the properties of
the blocks are given rather than the blocks themselves, e.g.
(Red Green Black Brown).  More generally a design could be specified
with some indefiniteness as to how many blocks of what color in
certain parts of the tower, e.g. as Red on top of Green on top of
several others none of which are Red or Green.

A tower may exist in a situation, e.g. as $exists((A B F D), s)$,
We could also specify the existence of designs as $exists1((Red
Green Brown Black),s)$.