SRS Category

This category is concerned with confluence of string rewrite systems.

Format

The input is a string rewrite system, specified in the basic TRS format.

The question to be answered is whether the string rewrite system is confluent. The first line of the output must be

• YES, indicating that the input system is confluent,
• NO, indicating that the input system is non-confluent,
• any other answer (e.g., MAYBE) indicates that the tool could not determine the status of the input problem.

In the first two cases, the output must be followed by justification that is understandable by a human expert.

Examples

1. (VAR x)
   (RULES
     f(f(x)) -> g(x)
   )
   

   The correct answer is NO and possible outputs include

   NO
   
   The peak f(g(x)) *<- f(f(f(x))) ->* g(f(x)) is not joinable.
   

   and

   MAYBE
   

2. (VAR x)
   (RULES
     f(f(x)) -> x
     f(x) -> f(f(x))
   )
   

   The correct answer is YES and a possible output is

   YES
   
   The addition of the redundant rules f(x) -> f(f(f(x))) and f(x) -> x makes
   the critical pairs of the SRS development closed. Hence the SRS is confluent.
   

Problem Selection

Problems are selected among those in COPS with the 'srs' tag.