String maps controlled by the first extension letter #
For an arbitrary right extension, the first new letter controls the module map across the old/new coordinate boundary. A negative first letter makes the old positions a subrepresentation, while a positive first letter makes their coordinate projection a quotient representation. Later letters may have either sign.
If the first appended letter is negative, every displayed-arrow output from an inherited position is still inherited, even after an arbitrary further tail.
The coordinate inclusion for a negative-boundary extension commutes with every displayed-arrow action.
A negative-boundary prefix inclusion is a morphism of quiver representations.
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In the opposite-module realization, the negative-boundary inclusion has the reversed natural-transformation direction.
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Descend the negative-boundary inclusion through the monomial relation quotient.
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The canonical inclusion associated to any extension whose first letter is negative, as a morphism of right modules.
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A negative-boundary map is a submodule inclusion.
Negative-boundary inclusions compose under further negative-boundary extension.
If the first appended letter is positive, no arrow action can travel from a non-inherited position back into an inherited position.
The coordinate projection for a positive-boundary extension commutes with every displayed-arrow action.
A positive-boundary coordinate projection is a morphism of quiver representations.
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In the opposite-module realization, the positive-boundary projection has the reversed natural-transformation direction.
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Descend the positive-boundary projection through the monomial relation quotient.
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The canonical projection associated to any extension whose first letter is positive, as a morphism of right modules.
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A positive-boundary map is a quotient projection.
Positive-boundary projections compose under further positive-boundary extension.