Multline latex output



Hi all:

Is there a   way of forcing multi-ilne  latex output (with line breaking).
Right now I use:

set_tex_environment_default ("\\begin{multline}\\displaystyle
", "
\\end{multline}");
tex(expr); 

No line breaking is included, thus, we get a latex compilation with errors
in each \begin{multline}.   


Thanks in advance.
-- 
Nuno  Lopes