Three theorems concerning principal AFLs

摘要

o(1)If every set in ℒ is a subset of a* and the empty word belongs to one of them, then Download : Download full-size image. One consequence is that Download : Download full-size image is always principal for Download : Download full-size image.(2)On the other hand, there is a language Download : Download full-size image such that Download : Download full-size image is not principal.(3)There are subsets J and K of a* such that Download : Download full-size image is not principal.