The blocks world is one of the most famous planning domains in artificial intelligence. The program was created by Terry Winograd and is a limited-domain natural-language system that can understand typed commands and move blocks around on a surface.

Imagine a set of cubes (blocks) sitting on a table. The goal is to build one or more vertical stacks of blocks. The catch is that only one block may be moved at a time: it may either be placed on the table or placed atop another block. Because of this, any blocks that are, at a given time, under another block cannot be moved.

The simplicity of this toy world lends itself readily to symbolic or classical A.I. approaches, in which the world is modeled as a set of abstract symbols which may be reasoned about.

Theses/projects which took place in Blocks World:

• Terry Winograd's SHRDLU
• Patrick Winston's structural concept learner

It is shown that the best version of blocks world is NP-hard(http://www.cs.pdx.edu/~bart/archive/cs510sps/hw/blocks-long.ps.gz).

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