\newenvironment{nam}[args]{begdef}{enddef}
  \renewenvironment{nam}[args]{begdef}{enddef}

  These commands define or redefine an environment.

   -  nam:  The name of the environment.  For \newenvironment there
      must be no currently defined environment by that name, and the
      command \nam must be undefined.  For \renewenvironment the
      environment must already be defined.

   -  args:  An integer from 1 to 9 denoting the number of arguments of
      the newly-defined environment.  The default is no arguments.

   -  begdef:  The text substituted for every occurrence of
      \begin{name}; a parameter of the form  n in cmd is replaced by
      the text of the nth argument when this substitution takes place.

   -  enddef:  The text substituted for every occurrence of \end{nam}.
      It may notcontain any argument parameters.