Hans Hagen
since this effect does not show op with cmtt, it looks like the lmtt fonts indeed have a ligature, which makes them somehow incompatible;
right. See for example cork-lmtt10.tfm (LIGTABLE (LABEL O 41) 1 (LIG O 140 O 275) (STOP) (LABEL O 77) 2 (LIG O 140 O 276) (STOP) (LABEL O 55) 3 (LIG O 55 O 25) 4 (LIG O 177 O 177) 5 (STOP) ) the first and second one is the standard TeX ?` and !` (perhaps I've got the accent wrong), that are also in cmtt. The third (3-4) is hyphen-hyphen->endash and the last one (3-5) hyphen-strangechar->strangechar (what is it? some other kind of hyphen?).
the best solution would be a \noligs primitives (also handy for xml)
:-) I think a lot of TeXhackers would like to see something like this.
an alternative is to have two tfm files, one for tt text with ligature building and one for verbatim, say:
cmtt10.tfm cmtv10.tfm
(cmvtt is already taken)
and some more of the font mess....
let's see what Jacko says ...
that would be good to hear. Patrick