\dncast{\u F (\cbvtocbpvty{A_1'}\times\cbvtocbpvty{A_2'})}{\u F \dyn}\defupcast{\u F (\cbvtocbpvty{A_1}\times\cbvtocbpvty{A_2})}{\u F \dyn}\cbvtocbpvcomp{(V_1,V_2)}\\
&\equidyn
\dncast{\u F (\cbvtocbpvty{A_1'}\times\cbvtocbpvty{A_2'})}{\u F (\dyn\times\dyn)}\defupcast{\u F (\cbvtocbpvty{A_1}\times\cbvtocbpvty{A_2})}{\u F (\dyn\times\dyn)}\cbvtocbpvcomp{(V_1,V_2)}\\
&\equidyn
\dncast{\u F (\cbvtocbpvty{A_1'}\times\cbvtocbpvty{A_2'})}{\u F (\dyn\times\dyn)}\defupcast{\u F (\cbvtocbpvty{A_1}\times\cbvtocbpvty{A_2})}{\u F (\dyn\times\dyn)}\ret(\cbvtocbpvval{V_1},\cbvtocbpvval{V_2})\\
&\equidyn
\dncast{\u F (\cbvtocbpvty{A_1'}\times\cbvtocbpvty{A_2'})}{\u F (\dyn\times\dyn)}(\ret\upcast{(\cbvtocbpvty{A_1}\times\cbvtocbpvty{A_2})}{(\dyn\times\dyn)}(\cbvtocbpvval{V_1},\cbvtocbpvval{V_2}))\\
&\equidyn
\dncast{\u F (\cbvtocbpvty{A_1'}\times\cbvtocbpvty{A_2'})}{\u F (\dyn\times\dyn)}\\
\dncast{\u F (\cbvtocbpvty{A_1'}\times\cbvtocbpvty{A_2'})}{\u F (\dyn\times\dyn)}(\ret (\upcast{\cbvtocbpvty{A_1}}\dyn{\cbvtocbpvval{V_1}}, \upcast{\cbvtocbpvty{A_2}}\dyn x_2))\\
\dncast{\u F (\cbvtocbpvty{A_1'} + \cbvtocbpvty{A_2'})}{\u F \dyn}\defupcast{\u F (\cbvtocbpvty{A_1} + \cbvtocbpvty{A_2})}{\u F \dyn}\cbvtocbpvcomp{(\inl V)}\\
&\equidyn
\dncast{\u F (\cbvtocbpvty{A_1'} + \cbvtocbpvty{A_2'})}{\u F (\dyn+\dyn)}\defupcast{\u F (\cbvtocbpvty{A_1} + \cbvtocbpvty{A_2})}{\u F (\dyn + \dyn)}\cbvtocbpvcomp{(\inl V)}\\
&\equidyn
\dncast{\u F (\cbvtocbpvty{A_1'} + \cbvtocbpvty{A_2'})}{\u F (\dyn+\dyn)}\defupcast{\u F (\cbvtocbpvty{A_1} + \cbvtocbpvty{A_2})}{\u F (\dyn+\dyn)}\ret(\inl\cbvtocbpvval V)\\
&\equidyn
\dncast{\u F (\cbvtocbpvty{A_1'} + \cbvtocbpvty{A_2'})}{\u F (\dyn+\dyn)}\ret\upcast{(\cbvtocbpvty{A_1} + \cbvtocbpvty{A_2})}{(\dyn+\dyn)}(\inl\cbvtocbpvval V)\\
&\equidyn
\dncast{\u F (\cbvtocbpvty{A_1'} + \cbvtocbpvty{A_2'})}{\u F (\dyn+\dyn)}\ret(\caseofXthenYelseZ{\inl\cbvtocbpvval V}{x_1. \inl\upcast{A_1}\dyn x_1}{x_2. \inr\upcast{A_2}\dyn x_2})\\
&\equidyn
\dncast{\u F (\cbvtocbpvty{A_1'} + \cbvtocbpvty{A_2'})}{\u F (\dyn+\dyn)}\ret(\inl\upcast{A_1}\dyn\cbvtocbpvval V)\\