DEFINITION arity_gen_cvoid_subst0()
TYPE =
       g:G
         .c:C
           .t:T
             .a:A
               .arity g c t a
                 d:C
                      .u:T
                        .i:nat
                          .getl i c (CHead d (Bind Void) u)
                            w:T.v:T.(subst0 i w t v)P:Prop.P
BODY =
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