tmac/tmac.an: define .MR in a groff compatible way

groff 1.23.0 added .MR to its -man macro package.  The NEWS file states
that the inclusion of the macro "was prompted by its introduction to
Plan 9 from User Space's troff in August 2020."  From d32deab it seems
that the name for Plan 9 from User Space's implementation was suggested
by groff maintainer G. Brandon Robinson.

Not sure if the intention was to make these definitions compatible, but
it would be nice if they were.

Currently, Plan 9 from User Space's .MR expects its second argument to
be parenthesized.  groff's .MR does not.  This results in extra
parentheses appearing in manual references when viewing Plan 9 from User
Space's manual pages on a system using groff.

1 files changed, 4 insertions, 4 deletions

diff --git a/man/man1/sed.1 b/man/man1/sed.1
index 8a892da1..d7142a56 100644
--- a/man/man1/sed.1
+++ b/man/man1/sed.1
@@ -78,7 +78,7 @@ that
 addresses the last line of input, or a context address,
 .BI / regular-expression / \f1,
 in the style of
-.MR regexp (7) ,
+.MR regexp 7 ,
 with the added convention that
 .L \en
 matches a
@@ -235,7 +235,7 @@ in the pattern space.
 Any character may be used instead of 
 .LR / .
 For a fuller description see
-.MR regexp (7) .
+.MR regexp 7 .
 .I Flags
 is zero or more of
 .RS
@@ -374,8 +374,8 @@ formatted manuscript.
 .IR grep (1), 
 .IR awk (1), 
 .IR lex (1), 
-.MR sam (1) ,
-.MR regexp (7)
+.MR sam 1 ,
+.MR regexp 7
 .br
 L. E. McMahon,
 `SED \(em A Non-interactive Text Editor',