[Merged by Bors] - feat (Algebra/Vertex/HVertexOperator) : Composite heterogeneous vertex operators

[ScottCarnahan]

This PR defines the composite of two heterogeneous vertex operators as a heterogeneous vertex operator, using iterated Hahn series. Composite vertex operators appear in some definitions of vertex algebras.

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• depends on: [Merged by Bors] - feat (RingTheory/HahnSeries) SMulZeroClass instances #13421 [SMulZeroClass]
• depends on: [Merged by Bors] - fix (Algebra/Vertex/HVertexOperator): rm defeq abuse in coeff function #13422 [rm defeq abuse]

[github-actions]

PR summary fe48b68ada

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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Declarations diff

+ comp
+ compHahnSeries
+ compHahnSeries_add
+ compHahnSeries_smul
+ comp_coeff

You can run this locally as follows

## summary with just the declaration names:
./scripts/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/declarations_diff.sh long <optional_commit>

[leanprover-community-mathlib4-bot]

This PR/issue depends on:

• [Merged by Bors] - feat (RingTheory/HahnSeries) SMulZeroClass instances #13421
• [Merged by Bors] - fix (Algebra/Vertex/HVertexOperator): rm defeq abuse in coeff function #13422
  By Dependent Issues (🤖). Happy coding!

[kim-em]

bors d+

[mathlib-bors]

✌️ ScottCarnahan can now approve this pull request. To approve and merge a pull request, simply reply with bors r+. More detailed instructions are available here.

[ScottCarnahan]

Thanks for the review!

bors r+

[mathlib-bors]

Pull request successfully merged into master.

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