.ig
Define a macro, then define an alias to it.
Redefining the original macro should redefine the alias as well,
and vice-versa.
..
.de xx
This is a macro.
.br
..
.als yy xx
.xx
.yy
.de xx
This is a macro, redefined the first time.
.br
..
.xx
.yy
.de yy
This is a macro, redefined the second time.
.br
..
.xx
.yy
