$\forall$${\it ds}$:$x$:Id fp$\rightarrow$ Type, ${\it da}$:$k$:Knd fp$\rightarrow$ Type, $l$:$\mathbb{N}$ List, $A$:ecl{-}trans{-}tuple\{i:l\}(${\it ds}$;${\it da}$).
\\[0ex]ecl{-}add{-}catch($A$;$l$) $\in$ ecl{-}trans{-}tuple\{i:l\}(${\it ds}$;${\it da}$)