also assure that location printing in Pretty is parenthesized correctly.

Somehow they went under the radar the first time. Now all of them should
have been fixed.

Strangely enough, as can be seen from the diff, the statement of
WP_parameter_gcd was thoroughly wrong. The old proof was actually matching
the new statement, so the file would never have compiled on its own. I
don't have any sensible explanation for such a breakage, except for gnomes
messing with bytes at night.