Section NaryDirect.
Context {I : finType} {P : pred I}.

Lemma directv_sumE {Ss : I -> addv_expr} (xunwrap := unwrap) :
reflect [/\ forall i, P i -> directv (unwrap (Ss i))
& directv (\sum_(i | P i) xunwrap (Ss i))]
(directv (\sum_(i | P i) unwrap (Ss i))).