aeval (EApp (Arr oSh _) (EApp _ (Builtin _ Map) f) xs) t a 
    | tX@(Arr xSh _) <- eAnn xs
    , Just xRnk <- staRnk xSh
    , Just ((ta0, rnk0), (ta1, rnk1)) <- mAA (eAnn f)
    , Just sz0 <- nSz ta0, Just sz1 <- nSz ta1 = do
    y <- nI; y0 <- nI
    szR <- nI; szY <- nI