query: extra IS

[Arnold Zwicky]

one of my grad students has been looking into "extra IS" sentences,
like
  The problem is is that we have to leave at 10.

bolinger 1986 is the only source we have on the phenomenon; does
anyone know anything else?

bolinger's citations have only one from a written source - a letter
by charles darwin! - and my student hasn't found any further written
examples of IS/WAS plus IS (except where ordinary syntax calls for
it, as in
   What the problem is is that we have to leave at 10.)
has anyone come across other written examples?

arnold (zwicky at csli.stanford.edu)