Help using DeclareUnicodeCharacter for russian

[ludvig-faddeev]

I am trying to declare unicode characters for russian

@macro ru

\DeclareUnicodeCharacter{1040}{\ensuremath\rua}
\DeclareUnicodeCharacter{1041}{\ensuremath\rube}
\DeclareUnicodeCharacter{1042}{\ensuremath\ruve}
\DeclareUnicodeCharacter{1043}{\ensuremath\rughe}
\DeclareUnicodeCharacter{1044}{\ensuremath\rude}
\DeclareUnicodeCharacter{1045}{\ensuremath\ruie}
\DeclareUnicodeCharacter{1046}{\ensuremath\ruzhe}
\DeclareUnicodeCharacter{1047}{\ensuremath\ruze}

@end macro


I am getting the following error

texi2pdf cyrillic.texi
This is pdfTeX, Version 3.14159265-2.6-1.40.18 (TeX Live 2017/Debian) 
(preloaded format=pdfetex)
 restricted \write18 enabled.
entering extended mode
(./cyrillic.texi (/texinfo.tex
Loading texinfo [version 2020-10-24.12]: pdf, fonts, markup, glyphs,
page headings, tables, conditionals, indexing, sectioning, toc, environments,
defuns, macros, cross references, insertions,
(/usr/share/texlive/texmf-dist/tex/generic/epsf/epsf.tex
This is `epsf.tex' v2.7.4 <14 February 2011>
) localization, formatting, and turning on texinfo input format.)
(../rama.texi
../rama.texi:56: Undefined control sequence.
@macrobody ...carg.DeclareUnicodeCharacter{1040}{
                                                  ensuremath@macarg.rua}^^M ...

@defmacro ...oup @noexpand @scanmacro {@macrobody
                                                  }}@or @expandafter @xdef @...
l.56 @end macro

?
../rama.texi:56: Emergency stop.
@macrobody ...carg.DeclareUnicodeCharacter{1040}{
                                                  ensuremath@macarg.rua}^^M ...

@defmacro ...oup @noexpand @scanmacro {@macrobody
                                                  }}@or @expandafter @xdef @...
l.56 @end macro

../rama.texi:56:  ==> Fatal error occurred, no output PDF file pro
duced!
Transcript written on cyrillic.log.
/usr/local/bin/texi2dvi: pdfetex exited with bad status, quitting.