Collational formula query

[Hoag Elaine <ELH@ABS.NLC-BNC.CA>]

I am cataloguing the following item:  Banque nationale precedee de l'examen
des principales banques publiques de l'Europe, et de la caisse d'escompte
... / par M. Gaudot -- Amsterdam : s.n., 1789.  The book is an octavo
printed on grape-watermark laid paper, and the copy is untrimmed in its
original paper covers, making it easy to see conjugacy, cancels, etc.

Following 2 preliminary unsigned leaves (not conjugate), collation follows
regularly in 8s from A-K.  Then there are 2 stubs (from which I believe the
2 prelim. leaves were cut); then 8 leaves of quire L, all signed regularly;
then 2 unsigned leaves that are conjugate with the 2 stubs that precede
gathering L.

I am uncertain how to construct a collational formula that will account for
the true makeup of the book--that gathering L is actually contained inside
an unsigned gathering of 4 leaves, from which the first 2 leaves have been
removed.  The best I can come up with on my own is: chi superscript 4
(-chi1,2; chi2+Lsuperscript 8).  This looks peculiar, though--particularly
the portion following the semicolon, because chi2 isn't really "there" to be
followed by anything.  I realize there are several ways I can construct the
formula if I ignore the actual structure of the book, but I would appreciate
any suggestions Exlibris subscribers can provide.

          Thank you,

          Elaine Hoag, Rare book cataloguer
          National Library of Canada, Ottawa
          elh@abs.nlc-bnc.ca