cless($E$;${\it pred?}$;${\it info}$;$e$;${\it e'}$) $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$rel\_plus($E$; ($\lambda$$e$,${\it e'}$. pred!($E$;${\it pred?}$;${\it info}$;$e$;${\it e'}$)))($e$,${\it e'}$)