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, 10 insertions, 10 deletions

diff --git a/man/man3/notify.3 b/man/man3/notify.3
index 9f2efb6d..74314d07 100644
--- a/man/man3/notify.3
+++ b/man/man3/notify.3
@@ -33,12 +33,12 @@ or writing on a closed pipe, a
 is posted to communicate the exception.
 A note may also be posted by another process
 via
-.MR postnote (3) .
+.MR postnote 3 .
 On Unix, notes are implemented as signals.
 .PP
 When a note is received, the action taken depends on the note.
 See
-.MR signal (7)
+.MR signal 7
 for the full description of the defaults.
 .PP
 The default actions may be overridden.
@@ -53,10 +53,10 @@ replaces the previous handler, if any.
 An argument of zero cancels a previous handler,
 restoring the default action.
 A
-.MR fork (2)
+.MR fork 2
 system call leaves the handler registered in
 both the parent and the child;
-.MR exec (3)
+.MR exec 3
 restores the default behavior.
 Handlers may not perform floating point operations.
 .PP
@@ -112,17 +112,17 @@ set up with
 using the
 .I notejmp
 function (see
-.MR setjmp (3) ).
+.MR setjmp 3 ).
 .PP
 Unix provides a fixed set of notes (typically there are 32) called
 .IR signals .
 It also allows a process to block certain notes from being delivered
 (see
-.MR sigprocmask (2) )
+.MR sigprocmask 2 )
 and to ignore certain notes by setting the signal hander to the special value
 .B SIG_IGN
 (see
-.MR signal (2) ).
+.MR signal 2 ).
 .I Noteenable
 and
 .I notedisable
@@ -137,7 +137,7 @@ is called upon receipt of the note; if the handler is not called, the note is di
 Regardless of the origin of the note or the presence of a handler,
 if the process is being debugged
 (see
-.MR ptrace (2) )
+.MR ptrace 2 )
 the arrival of a note puts the process in the
 .B Stopped
 state and awakens the debugger.
@@ -252,7 +252,7 @@ are usually generated by the operating system.
 .br
 .B \*9/src/lib9/atnotify.c
 .SH SEE ALSO
-.MR intro (3) ,
+.MR intro 3 ,
 .I notejmp
 in
-.MR setjmp (3)
+.MR setjmp 3