Localization of (in)consistencies by monotone reducing automata

A reducing automaton (red-automaton) is a deterministic automaton proposed for checking word and sub-word correctness by the use of analysis by reduction. Its monotone version characterizes the class of deterministic context-free languages (DCFL). We propose a method for a construction of a deterministic monotone enhancement of any monotone reducing automaton which is able with the help of special auxiliary symbols to localize its prefix and post-prefix (in)consistencies, and certain types of reducing conflicts. In other words this method ensures a robust analysis by reduction without spurious error messages. We formulate natural conditions for which this method ensures the localization of all prefix and post-prefix inconsistencies in any (incorrect) word with respect to a DCFL.