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$\vdash$  \=$\forall$$A$, $B$, $C$:Type, $g$:($A$$\rightarrow$($B$ + Top)), $f$:($B$$\rightarrow$($C$ + Top)).\+
\\[0ex]p{-}inject($A$;$B$;$g$) $\Rightarrow$ p{-}inject($B$;$C$;$f$) $\Rightarrow$ p{-}inject($A$;$C$;$f$ o $g$  )
\-
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