Existence of NL languages not recognized by REWB (conjecture)

Establish that there exists a language in NL (nondeterministic log-space) that is not recognized by regular expressions with backreferences (REWB), thereby proving REWB is a strict subset of NL.

Background

Earlier in the paper, the author shows that REWB contains an NL-complete language (TAGAP), demonstrating that REWB is powerful within NL. However, whether REWB spans all of NL remains unresolved.

The conclusion explicitly conjectures that some NL languages are not recognizable by REWB. Proving this would sharpen the placement of REWB within the NL landscape and clarify the limits of backreferences without lookaheads.