Semiretracts - a counterexample and some results
In the paper (Theoret. Comput. Sci. 237 (2000)) Anderson present a theorem which characterizes any semiretract S by means of two retracts R-alpha and R-omega. The first part of the paper contains a counterexample for this characterization. Then some results are presented which finally lead to the theorem which determines for a given semiretract S the minimal number of retracts R-1,...,R-m such that the equality S = boolean AND(i=1)(m) R-i holds. (C) 2003 Elsevier B.V. All rights reserved.
semiretract retract free monoid