Evaluation at the projective labels: full faithfulness (Lemma 2.9) #
Construction 2.8 (con:projective-algebra): A₀ = ⊕_{x,y} D(P_y, P_x), the
category algebra of the projective labels, and evaluation sends X to the
module with components C(P_x, X). Lemma 2.9 (first part,
graded-category.tex): under the vanishings for modules killed by e,
"P ↦ Pe is fully faithful on proj Λ". The manuscript proves this with the
multiplication map (Me) ⊗_{Λ_e} eΛ → M, whose kernel and cokernel are killed
by e, and the vanishings. We use the same two steps without the tensor
product: a map g on the e-parts is defined on the submodule generated by
the e-part by ∑ λ_i m_i ↦ ∑ λ_i g(m_i), well defined because the
discrepancy generates a submodule killed by e (Hom-vanishing), and it extends
to the whole module because the quotient is killed by e (Ext¹-vanishing).
add C is represented by finite families of labels; maps between families are
matrices of morphisms.
The projective labels.
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The projective labels as a family of objects.
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Extension by zero from the projective labels.
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Restriction to the projective labels.
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The P × P block of an element of Λ.
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Elements with rows in P act on the e-part through their P × P
block.
e_p m lies in the image of extension by zero.
Finite families #
The evaluation ⊕_j C(P_-, Z j) of a family.
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The Λ-linear map of a matrix.
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The A₀-linear map of a matrix: evaluation.
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Extension by zero, componentwise.
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The matrix of a Λ-linear map between families (Yoneda).
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The e-part of a family generates a submodule whose quotient is killed by e.
Evaluation is faithful on add C (Lemma 2.9).
Evaluation is full on add C (Lemma 2.9).