A description of text processing work at Bell Labs, including the use of
trigrams for spell checking, readability analysis, and word class
assignment was published in the BSTJ.

L. E. McMahon; L. L. Cherry; R. Morris. Statistical text processing. The
Bell System Technical Journal, 57(6):2137-2154, July-Aug. 1978.
DOI: 10.1002/j.1538-7305.1978.tb02146.x

You can find it openly available online at:
https://archive.org/details/bstj57-6-2137/mode/2up

The article was part of an amazing special issue of BSTJ devoted to
Unix.  A second such issue, 63(8) was published on October 1984.  In the
late 1980s both issues were also sold as books by Prentice Hall under
the title "UNIX System Readings and Applications".  I broke the bank
buying them as a student, but didn't regret it.

Diomidis - https://www.spinellis.gr

On 16-Feb-22 2:09, George Michaelson wrote:
> The trigraph spelling checker sounds wonderful.