Socle rejection at a projective-injective module #
Besides making P / soc(P) projective, rejection of the embedded socle of a
non-simple indecomposable projective-injective P makes rad(P) injective.
This file proves that assertion first in the full ambient subcategory
annihilated by the socle ideal and then transports it to the literal quotient
algebra.
The finite tau-category of the literal quotient by an arbitrary ideal, with Noetherianity discharged from finite dimensionality.
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The chosen ambient minimal right almost-split decomposition, reindexed by a finite ordinal.
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A non-simple projective-injective vertex has exactly one incoming right-middle occurrence.
Away from P / soc(P), the ambient minimal right almost-split middle
term contains no copy of the rejected projective-injective P.
Away from the exceptional endpoint P / soc(P), the entire ambient
minimal right almost-split middle term is already a module over the socle
quotient.
At every surviving endpoint other than P / soc(P), projectivity in
the annihilated full subcategory is equivalent to ambient projectivity.
The same ordinary-vertex projectivity comparison over the literal socle quotient algebra.
Intrinsic socle-quotient labels are exactly the ambient labels other than the rejected projective-injective label.
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The finite-ordinal quotient labels are equivalent to the ambient labels surviving rejection.
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The finite quotient-skeleton label corresponding to an ambient label other than the rejected projective-injective.
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The finite quotient representative of a surviving ambient label is the literal quotient module obtained from that ambient object.
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Every other projective-injective vertex remains projective-injective
after rejecting the socle of p.
A distinct ambient nonsimple projective-injective remains nonsimple as a module over the one-step socle quotient.
The replacement vertex in the finite-ordinal quotient skeleton.
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The replacement vertex is nonprojective in the ambient finite-tau presentation.
The replacement vertex is projective in the rejected finite-tau presentation.
In the finite-tau presentations, projectivity is unchanged at every ordinary surviving endpoint.
Every ordinary surviving endpoint has the same incoming right-mesh arity before and after rejection of the projective-injective socle.
The radical boundary object is not injective in the ambient module category.
The embedded socle ideal annihilates the radical boundary object.
The maximal submodule of the rejected projective-injective annihilated by its embedded socle ideal is its Jacobson radical.
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The restricted source at the exceptional endpoint has a displayed
indecomposable decomposition with the same number of terms as the ambient
right almost-split middle term. The rejected summand becomes rad(P);
every other summand is already annihilated by the socle ideal.
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The radical boundary object bundled in the full annihilated subcategory.
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After socle rejection, rad(P) is injective in the annihilated ambient
full subcategory.
The literal quotient-algebra module corresponding to rad(P).
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The transported radical boundary module is injective over the literal socle quotient algebra.
The intrinsic quotient-skeleton label represented by rad(P).
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The literal transported radical is isomorphic to its intrinsic quotient-skeleton representative.
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The intrinsic radical label is injective over the socle quotient algebra.
At the exceptional endpoint P / soc(P), socle rejection removes
exactly one indecomposable occurrence from the incoming right mesh.
The complete finite-tau rejection profile produced by removing the socle of one non-simple indecomposable projective-injective module.
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Removing the socle of one non-simple indecomposable projective-injective preserves the finite Auslander--Reiten Euler magnitude.