reducible configuration

reducible configuration

[ri′dü·sə·bəl kən‚fig·yə′rā·shən]
(mathematics)
A graph such that the four-colorability of any planar graph containing the configuration can be deduced from the four-colorability of planar graphs with fewer vertices.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.