glues(${\it es}$; $B$; $g$; $f$; ${\it Ia}$; ${\it Ib}$) $\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$$g$ glues ${\it Ia}$:$\lambda$$e$,${\it e'}$. $e$ $\leq$loc ${\it e'}$  $--$$f$$\rightarrow$ ${\it Ib}$:$\lambda$$e$,${\it e'}$. $e$ $\leq$loc ${\it e'}$