Redefine macro in macro with parameter

Question

I've been trying this for hours now. Probably is something simple I missed...

I have a macro \newcommand{\cf}[1]{\footnote{Cf. #1}} (usage usually \cf{\cite{xx}}). Now I want to extend it, that it remembers which reference I used last, and if it is the same again, does not print the citation but "Ibd." instead.

Thus I modified it like

\newcommand{\cf}[1]{
  Cf.    
  \ifthenelse{\equals{\SVE}{#1}}{%
    ibd.}{%
    #1
    \def\SVE#1
  }
}

But that does not work. \SVE remains empty (or however I initialized it first). I experimented a lot till now, putting \expandafters, \noexpands,... around like crazy... But no result.

-- Edit:

Heres the full code copied:

\documentclass{article}

% somewhere in my preamble
\usepackage{ifthen}
\newcommand{\LLfootnoteLastCite}{}
\newcommand\LLfootnoteCite[1]{%
    \ifthenelse{\equal{\LLfootnoteLastCite}{#1}}{%
        ibd.}{%
        #1%
        \def\LLfootnoteLastCite{#1}%
    }%
}
\newcommand{\LLfootnote}[3]{\footnote{#3~#2\ifx#10\else, S. #1\fi.}}

% the exposed commands
\newcommand{\vgl}[2][0]{\LLfootnote{#1}{\LLfootnoteCite{#2}}{Vgl.}}


% small working example
\begin{document}
  This is a\vgl{\cite{Reference}}. And this is the second\vgl{\cite{Reference}}. And this is a third\vgl{\cite{Reference2}}
\end{document}

Answer 1

\documentclass{article}

\usepackage{ifthen}

\newcommand\SVE{}% initialize

\newcommand{\cf}[1]{%you need this %
  Cf.    
  \ifthenelse{\equal% \equal not \equals
       {\SVE}{#1}}{%
    ibd.}{%
    #1% you need thi s%
    \def\SVE{#1}% braces are mandatory for \def
  }% you need this %
}
\begin{document}

\cf{aaa} \cf{aaa} \cf{zzz} \cf{zzz}

\end{document}