An expression in NLPrSS are sequences defined recursively as \(()\),\(\Omega_n\) for an arbitrary natural number \(n\), or a sequence thereof.
\(\&\) denotes concatenation, \(\#_n\) denotes a sequence variable where \(n\) is an arbitrary natural number (\(n\) may be omitted if there is only one).
Let \(S\) be an NLPrSS expression. Define recursively a function \(\mathrm{cof}\) taking an NLPrSS expression and giving an NLPrSS expression as follows:
- Suppose \(S=()\)
- \(\mathrm{cof}(S)=()\)
- Suppose \(S=\#\&()\)
- \(\mathrm{cof}(S)=(())\)
- Suppose \(S=\#_0\&(\#_1\&())\)
- \(\mathrm{cof}(S)=((),(()))\)
W.I.P.