Text Formatting ⇒ weird problem with ifthenelse and subsections

[poppi]

Hello dear community,
I want to use optional bracketed tags in subsection-headlines, e.g. something like:

Definition (Definitionname)

whereas "Definition" is the constant part and "(Definitionname)" is an additional tag; if no tag is specified, just the constant part shall be created:

Definition

The LaTex code to invoke such a Definition-environment shall look like:

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  \begin{definition}{Definitionname}{Some text ...}
  \end{definition}

for an additional tag, or

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  \begin{definition}{}{Some text ...}
  \end{definition}

for no given tag. For the optional part, I use the ifthen-package, but it seems that it cannot be used in subsections? The LaTex-Code below shows the related part of my document, and it works for "always-defined" tags, since I commented out the failure-part for optional tags.

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\documentclass[a4paper,10pt]{article}

\usepackage{ifthen}

\newcommand{\bracketedname}[1]{
%  \ifthenelse{\equal{#1}{\empty}}{ }{\ (#1)}
  (#1)
}

\newenvironment{definition}[2]{
  \subsubsection{Definition \bracketedname{#1}} #2
}{}

\begin{document}

\begin{definition}{Definitionname}{Some text ...}
\end{definition}

\end{document}

If I activate the line

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%  \ifthenelse{\equal{#1}{\empty}}{ }{\ (#1)}

instead of using the line

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  (#1)

I get the following error message:

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! Undefined control sequence.
<argument> \equal 
                  {Definitionname}{\empty }
l.16 ...definition}{Definitionname}{Some text ...

Has anyone a solution for this? I would be very thankful for that

Thank you in advance,
poppi

[localghost]

Problem mit ifthenelse und Subsections - mrunix.de