Known Problems with some *roff versions

If you encounter the error:

Unknown escape sequence in input: 33, 133

when trying to create op.txt then set the GROFF_NO_SGR environment
variable (see grotty(1) man page), e.g.,

csh% setenv GROFF_NO_SGR 1
sh$ GROFF_NO_SGR=1; export GROFF_NO_SGR

$Id: README 1073 2021-06-27 05:01:23Z  $