feat(SimpleGraph/Hamiltonian): a graph is Hamiltonian iff there's a Hamiltonian path with adjacent endpoints

[SnirBroshi]

and some other Hamiltonian lemmas.

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[github-actions]

PR summary f89dabe29b

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 (regex)

+ IsHamiltonianCycle.isHamiltonian_dropLast
+ Walk.IsHamiltonian.isHamiltonian_of_adj
+ isHamiltonianCycle_copy
+ isHamiltonianCycle_iff_isHamiltonian_tail_and_le_card
+ isHamiltonian_copy
+ isHamiltonian_dropLast_iff
+ isHamiltonian_iff_exists_adj_and_isHamiltonian

You can run this locally as follows

## from your `mathlib4` directory:
git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

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

## more verbose report:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh in the mathlib-ci repository contains some details about this script.

Declarations diff (Lean)

✅ Lean-aware diff — post-build, computed from the Lean environment (commit f89dabe).

• +7 new declarations
• −0 removed declarations

+SimpleGraph.Walk.IsHamiltonian.isHamiltonian_of_adj
+SimpleGraph.Walk.IsHamiltonianCycle.isHamiltonian_dropLast
+SimpleGraph.Walk.isHamiltonianCycle_copy
+SimpleGraph.Walk.isHamiltonianCycle_iff_isHamiltonian_tail_and_le_card
+SimpleGraph.Walk.isHamiltonian_copy
+SimpleGraph.Walk.isHamiltonian_dropLast_iff
+SimpleGraph.isHamiltonian_iff_exists_adj_and_isHamiltonian

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No changes to strong technical debt.

No changes to weak technical debt.

Current commit f89dabe29b
Reference commit e2361c1beb

This script lives in the mathlib-ci repository. To run it locally, from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci
../mathlib-ci/scripts/reporting/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).