Kernekoncepter
Commutative N-polyregular functions can be effectively characterized and their membership is decidable. This resolves an open conjecture on the relationship between star-free N-polyregular functions and star-free Z-polyregular functions.
Resumé
The paper addresses two main questions regarding commutative N-polyregular functions:
- Decidability of membership:
- It is shown that it is decidable whether a given commutative Z-polyregular function is an N-polyregular function.
- This is achieved by providing a semantic characterization of N-rational polynomials, which are a subclass of N-polyregular functions.
- A counter-example is provided to refute a previous result on the characterization of N-rational polynomials.
- Decidability of aperiodicity:
- It is shown that for commutative N-polyregular functions, being ultimately polynomial is equivalent to being star-free.
- This resolves an open conjecture on the relationship between star-free N-polyregular functions and star-free Z-polyregular functions.
- The decidability of this property follows from the effective conversions between the different characterizations.
Additionally, the paper introduces the notion of a residual transducer as a canonical model of computation for N-polyregular functions, which is conjectured to be computable for all N-polyregular functions.