Tame transition data: the graph of a transition closes only on the graph #
For a normalized transition datum P (Hironaka.AnalyticSpace.Glue.Normalize) between the local
complexifications (Y_i, f_i), (Y_j, f_j) over V, write P.graph ⊆ Y_i × Y_j for the graph of
the transition on its domain, P.realGraph = {(f_i x, f_j x) : x ∈ V} and
P.outer = f_i(U_i ∖ V) × f_j(U_j ∖ V) (a closed set, imageDiff). P is tame when
closure P.graph avoids P.outer. Then:
graph_inter_real_eq: the graph meets the real points only in the real graph;closure_graph_inter_real_subset: for tameP, the closure of the graph meetsR_i × R_jonly in the graph (the three cases ofclosure_graphOn_inter_prod_subset,Hironaka.AnalyticSpace.Glue.GraphClosure);exists_tame: for every datum overV = U_i ⊓ U_jthere is a tame datum overV(the domain is shrunk byexists_isOpen_graphOn_closure_disjoint, the transition restricted alongKIso.restrictToImage, defined here: the restriction of aK-isomorphism of open subspaces to a smaller open subset and its image).
Conventions. The closedness of the real graph uses V = U_i ⊓ U_j (the real graph is the image of
the diagonal of U_i × U_j under the closed embedding f_i × f_j); Y_i × Y_j is metrizable
(analytic spaces are regular and second countable). For V = ∅ the real graph is empty,
outer = R_i × R_j, and tameness says that the closure of the graph contains no pair of real
points.
Tameness is the first arrangement in the gluing of local complexifications [BW59, Proposition 1]: it is what makes the transition graphs of the shrunk pieces closed, hence the glued space Hausdorff.
Restricting a K-isomorphism of open subspaces to a smaller open and its image #
The restriction of a K-isomorphism A | Ω ≅ B | Ω' to an open S ≤ Ω and its image S'.
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The graph of a transition datum #
The transition as a map on its domain, valued in Y_j.
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- P.toMap y = ↑(AnalyticSpace.KLocallyRingedSpace.Hom.toFun P.e.hom y)
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The inverse transition as a map on its domain, valued in Y_i.
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- P.invMap z = ↑(AnalyticSpace.KLocallyRingedSpace.Hom.toFun P.e.inv z)
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The graph of the transition.
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- P.graph = AnalyticSpace.Glue.graphOn P.toMap ↑P.Ωi
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The real graph {(f_i x, f_j x) : x ∈ V}.
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The pairs of real points outside both domains, f_i(U_i ∖ V) × f_j(U_j ∖ V).
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A datum is tame when the closure of its graph avoids outer.
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For V = U_i ⊓ U_j the real graph is closed: it is the image of the diagonal of U_i × U_j
under the closed embedding f_i × f_j.
A real point of Y_i outside the domain lies over U_i ∖ V.
The graph meets the real points only in the real graph.
For a tame datum the closure of the graph meets the real points only in the graph.