The analytic realization of an open subfan #
A face-closed set of cones of a regular fan is itself a regular fan, TauCeti.Toric.Fan.subfan.
The affine chart of one of its cones and the affine chart of the same cone in the ambient fan have
the same underlying complex points, and their monomial-embedding topologies agree because that
topology does not depend on the chosen finite generating family. These identity-on-points chart
comparisons commute with the face maps of the two chart diagrams, so they glue to a continuous map
from the realization of the subfan to the ambient realization.
Composed with the inclusion of the chart of a cone of the subfan, this map is the chart comparison followed by the inclusion of the chart of the same cone in the ambient realization. It is an open embedding whose image is the union of the ambient charts of the cones of the subfan. No nonemptiness assumption is made on the set of cones of the subfan.
Main declarations #
TauCeti.Toric.Fan.subfanAnalyticChartMap: the identity-on-points homeomorphism between the chart of a cone of a subfan and the chart of the same cone in the ambient fan.TauCeti.Toric.Fan.subfanAnalyticMap: the map from the analytic realization of a subfan to the ambient analytic realization.TauCeti.Toric.Fan.analyticAffineChartι_comp_subfanAnalyticMap: its chart formula.TauCeti.Toric.Fan.range_subfanAnalyticMap: its image is the union of the ambient charts of the cones of the subfan.TauCeti.Toric.Fan.isOpenEmbedding_subfanAnalyticMap: it is an open embedding.
References #
- W. Fulton, Introduction to Toric Varieties, §§1.4 and 2.4.
- D. Cox, J. Little and H. Schenck, Toric Varieties, §3.1.
- The construction of the glued map and the proofs of injectivity, openness and the range follow
Mathlib's
TopCat.GlueData.fromOpenSubsetsGlue(Mathlib.Topology.Gluing).
Chart comparisons #
The chart of a cone of a subfan and the chart of the same cone in the ambient fan carry the same topology.
The identity-on-points homeomorphism from the chart of a cone of a subfan to the chart of the same cone in the ambient fan.
Instances For
The chart comparison of a subfan is the identity on complex points.
The inverse chart comparison of a subfan is the identity on complex points.
The chart comparisons of a subfan commute with the face maps of the two chart diagrams.
The glued map #
The map from the analytic realization of a subfan to the analytic realization of the ambient fan, glued from the chart comparisons followed by the ambient chart inclusions.
Instances For
On the chart of a cone of a subfan, the subfan map is the chart comparison followed by the inclusion of the chart of the same cone in the ambient realization.
On the chart of a cone of a subfan, the subfan map is the chart comparison followed by the inclusion of the chart of the same cone in the ambient realization.
On a point of the chart of a cone of a subfan, the subfan map is the inclusion of the same complex point in the chart of that cone in the ambient realization.
The subfan map is injective.
The image of the subfan map is the union of the ambient charts of the cones of the subfan.
The subfan map is an open map.
The map from the analytic realization of a subfan to the ambient analytic realization is an open embedding.