Irreducible mixed hook--cohook boundary sequences #
The generic mixed boundary square retains only the signs of its four boundary maps. Here an actual left cohook deletion and right hook are replayed with their maximal arms intact, so all four maps are literal hook or cohook maps.
A left cohook deletion is literally the left cohook extension which reattaches the deleted prefix.
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Sign-preserving replay of the right hook after deleting the left cohook prefix.
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The sign-preserving hook replay and the generic positive-boundary replay produce the same word.
The shortened word carries a literal maximal right hook to the mixed square's right result.
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Sign-preserving replay of the deleted left cohook after the restricted right-hook word is reversed.
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The sign-preserving cohook replay and the generic negative-boundary replay produce the same reversed corner word.
The restricted right-hook word carries a literal maximal left cohook to the common corner.
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The mixed boundary square rebuilt from four literal maximal maps: the replayed right hook, the original left cohook, the replayed left cohook, and the original right hook.
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The manuscript input of a left cohook deletion and a right hook, rebuilt as the literal four-maximal-map mixed square.
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The four-maximal-map mixed boundary complex in the finite-dimensional module category.
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The finite four-maximal-map mixed boundary complex is exact.
In the distinct-middle case, the replayed right hook and left cohook assemble to the irreducible first differential of the mixed sequence.
In the distinct-middle case, the original left cohook and transported right hook assemble to the irreducible second differential.
In the distinct-middle case, the literal finite mixed boundary complex is short exact.
The two middle modules of a mixed cohook--hook square cannot be isomorphic: the common corner is strictly longer than the base word.
The first differential of the mixed cohook--hook complex is unconditionally irreducible.
The second differential of the mixed cohook--hook complex is unconditionally irreducible.
The literal mixed cohook--hook complex is unconditionally short exact.
The finite literal mixed complex in the manuscript's deletion--hook input form.
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The first differential in the deletion--hook input form is irreducible.
The second differential in the deletion--hook input form is irreducible.
A left cohook deletion and a right hook give the literal short exact mixed boundary sequence.