      \fitem{occurs}(tab \emph{or} map \emph{or} string, \vValue): returns
      the first index or the first key whose value equals the second
      argument. For example
      \begin{lstlisting}
            @occurs(["a", "b", "c", "a", "b"], "b") ->1
            @occurs("xyz", "z")  ->2
            @occurs(map{ ("zero", 0), ("null", 0), ("void", 0) }, 0)  ->"null"
      \end{lstlisting}
      In the last example, the answer \code{"null"} is returned because
      \code{"null" < "void" < "zero"}. 
      %% 
      See also \acode{count}, \acode{find} and \acode{member}.




      %%% -------------------------------------------------------

