[mlochbaum]

The left argument is a window length. Windowed reduction groups the argument into overlapping windows with that length and does a reduction on each one of them. So if y has row length n, (n ?/ y) is the same as (?/ y) but the rank isn't reduced by one (there's an extra 1 at the end of the shape). For a numeric vector you can use ,/ as a windowed reduction to see the subvectors that are reduced over, but for a nested vector that trick doesn't quite work because it messes up the nesting.

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