diff --git a/FormalConjectures/WrittenOnTheWallII/GraphConjecture189.lean b/FormalConjectures/WrittenOnTheWallII/GraphConjecture189.lean new file mode 100644 index 000000000..a9e5796fa --- /dev/null +++ b/FormalConjectures/WrittenOnTheWallII/GraphConjecture189.lean @@ -0,0 +1,81 @@ +/- +Copyright 2025 The Formal Conjectures Authors. + +Licensed under the Apache License, Version 2.0 (the "License"); +you may not use this file except in compliance with the License. +You may obtain a copy of the License at + + https://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, software +distributed under the License is distributed on an "AS IS" BASIS, +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +See the License for the specific language governing permissions and +limitations under the License. +-/ + +import FormalConjectures.Util.ProblemImports + +/-! +# Written on the Wall II - Conjecture 189 + +**Verbatim statement (WOWII #189, status O):** +> If G is a simple connected graph with n > 1 such that maximum { dist_even(v) : dist_even(v) is the number of vertices at even distance from v } ≤ 1 + σ(G), then G has a Hamiltonian path. + +**Source:** http://cms.uhd.edu/faculty/delavinae/research/wowII/all.html#conj189 + + +*Reference:* +[E. DeLaVina, Written on the Wall II, Conjectures of Graffiti.pc](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) +-/ + +namespace WrittenOnTheWallII.GraphConjecture189 + +open Classical SimpleGraph + +variable {α : Type*} [Fintype α] [DecidableEq α] [Nontrivial α] + +/-- `distEven G v` counts the number of vertices at even distance from `v` in `G`. -/ +noncomputable def distEven (G : SimpleGraph α) (v : α) : ℕ := + (Finset.univ.filter (fun w => Even (G.dist v w))).card + +/-- The **second-smallest degree** of `G`'s degree sequence — DeLaVina's +`σ(G)` per the WOWII definitions popup (defEntry 65): "order the degree +sequence in nondecreasing order `d_1 ≤ d_2 ≤ … ≤ d_n`, the second smallest +degree of the sequence is the 2nd entry". For graphs with `n ≤ 1` we +conventionally return `0`. -/ +noncomputable def secondSmallestDegree (G : SimpleGraph α) [DecidableRel G.Adj] : ℕ := + (degreeSequence G).getD 1 0 + +/-- +WOWII [Conjecture 189](http://cms.uhd.edu/faculty/delavinae/research/wowII/all.html#conj189) +(status O): + +For a simple connected graph `G`, if `max_v distEven(v) ≤ 1 + σ(G)`, +then `G` has a Hamiltonian path. + +Here `distEven(v)` is the number of vertices at even distance from `v`, and +`σ(G)` is the **second-smallest degree** of `G`'s degree sequence (per +WOWII defEntry 65). +-/ +@[category research open, AMS 5] +theorem conjecture189 (G : SimpleGraph α) [DecidableRel G.Adj] (h : G.Connected) + (hσ : (Finset.univ.image (distEven G)).max' (by simp) ≤ 1 + secondSmallestDegree G) : + ∃ a b : α, ∃ p : G.Walk a b, p.IsHamiltonian := by + sorry + +-- Sanity checks + +/-- The second-smallest degree is nonneg. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) [DecidableRel G.Adj] : + 0 ≤ secondSmallestDegree G := Nat.zero_le _ + +/-- `distEven G v` is positive for any vertex `v`. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) (v : Fin 3) : 0 < distEven G v := by + unfold distEven + apply Finset.card_pos.mpr + exact ⟨v, Finset.mem_filter.mpr ⟨Finset.mem_univ _, ⟨0, by simp [SimpleGraph.dist_self]⟩⟩⟩ + +end WrittenOnTheWallII.GraphConjecture189 diff --git a/FormalConjectures/WrittenOnTheWallII/GraphConjecture199.lean b/FormalConjectures/WrittenOnTheWallII/GraphConjecture199.lean new file mode 100644 index 000000000..88beb777c --- /dev/null +++ b/FormalConjectures/WrittenOnTheWallII/GraphConjecture199.lean @@ -0,0 +1,75 @@ +/- +Copyright 2025 The Formal Conjectures Authors. + +Licensed under the Apache License, Version 2.0 (the "License"); +you may not use this file except in compliance with the License. +You may obtain a copy of the License at + + https://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, software +distributed under the License is distributed on an "AS IS" BASIS, +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +See the License for the specific language governing permissions and +limitations under the License. +-/ + +import FormalConjectures.Util.ProblemImports + +/-! +# Written on the Wall II - Conjecture 199 + +**Verbatim statement (WOWII #199, status O):** +> If G is a simple connected graph with n > 1 such that tree(G) - 2 ≤ κ(G), then G has a Hamiltonian path. + +**Source:** http://cms.uhd.edu/faculty/delavinae/research/wowII/all.html#conj199 + + +*Reference:* +[E. DeLaVina, Written on the Wall II, Conjectures of Graffiti.pc](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) +-/ + +namespace WrittenOnTheWallII.GraphConjecture199 + +open Classical SimpleGraph + +variable {α : Type*} [Fintype α] [DecidableEq α] [Nontrivial α] + +/-- `largestInducedTreeSize G` is the number of vertices in a largest induced subtree of `G`. -/ +noncomputable def largestInducedTreeSize (G : SimpleGraph α) : ℕ := + sSup { n | ∃ s : Finset α, s.card = n ∧ (G.induce (s : Set α)).IsTree } + +/-- The vertex connectivity `κ(G)`: the minimum number of vertices whose removal +disconnects the graph (or `n - 1` when the graph is complete). +Vertex connectivity is not yet in Mathlib; we define it here as the minimum size of +a vertex separator, where removing `S` leaves the induced subgraph on `Sᶜ` disconnected. +-- TODO: replace with a Mathlib definition when one becomes available. -/ +noncomputable def vertexConnectivity (G : SimpleGraph α) : ℕ := + if Fintype.card α ≤ 1 then 0 + else sInf { k | ∃ S : Finset α, S.card = k ∧ + (¬(G.induce (↑Sᶜ : Set α)).Connected ∨ S.card = Fintype.card α - 1) } + +/-- +WOWII [Conjecture 199](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) + +For a simple connected graph `G`, if `tree(G) - 2 ≤ κ(G)`, then `G` has a Hamiltonian path. +Here `tree(G)` is the number of vertices in a largest induced tree and +`κ(G) = vertexConnectivity G` is the vertex connectivity of `G`. +-/ +@[category research open, AMS 5] +theorem conjecture199 (G : SimpleGraph α) (h : G.Connected) + (hκ : largestInducedTreeSize G - 2 ≤ vertexConnectivity G) : + ∃ a b : α, ∃ p : G.Walk a b, p.IsHamiltonian := by + sorry + +-- Sanity checks + +/-- The `largestInducedTreeSize` is nonneg. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) : 0 ≤ largestInducedTreeSize G := Nat.zero_le _ + +/-- The vertex connectivity is nonneg. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) : 0 ≤ vertexConnectivity G := Nat.zero_le _ + +end WrittenOnTheWallII.GraphConjecture199 diff --git a/FormalConjectures/WrittenOnTheWallII/GraphConjecture24.lean b/FormalConjectures/WrittenOnTheWallII/GraphConjecture24.lean new file mode 100644 index 000000000..40fffaf67 --- /dev/null +++ b/FormalConjectures/WrittenOnTheWallII/GraphConjecture24.lean @@ -0,0 +1,78 @@ +/- +Copyright 2025 The Formal Conjectures Authors. + +Licensed under the Apache License, Version 2.0 (the "License"); +you may not use this file except in compliance with the License. +You may obtain a copy of the License at + + https://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, software +distributed under the License is distributed on an "AS IS" BASIS, +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +See the License for the specific language governing permissions and +limitations under the License. +-/ + +import FormalConjectures.Util.ProblemImports + +/-! +# Written on the Wall II - Conjecture 24 + +**Verbatim statement (WOWII #24, status F):** +> If G is a simple connected graph, then b(G) ≥ λ(G) + CEIL[minimum of dist_even(v)/3] + +**Source:** http://cms.uhd.edu/faculty/delavinae/research/wowII/all.html#conj24 + +This conjecture is **disproved** on the WOWII page (status F). Following the +upstream pattern established in #3823 for the closely related Conjecture 23, +we record the disproof using `answer(False) ↔ ...`. + +*Reference:* +[E. DeLaVina, Written on the Wall II, Conjectures of Graffiti.pc](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) +-/ + +namespace WrittenOnTheWallII.GraphConjecture24 + +open Classical SimpleGraph + +/-- `distEven G v` counts the number of vertices at even distance from `v` in `G`. +Distance 0 (the vertex itself) is even, so `distEven G v ≥ 1`. -/ +noncomputable def distEven {α : Type*} [Fintype α] + (G : SimpleGraph α) (v : α) : ℕ := + (Finset.univ.filter (fun w => Even (G.dist v w))).card + +/-- +WOWII [Conjecture 24](http://cms.uhd.edu/faculty/delavinae/research/wowII/all.html#conj24) +(status F, disproved): + +For every finite simple connected graph `G`, +`b(G) ≥ λ(G) + ⌈(min_v dist_even(v)) / 3⌉` +where `b(G)` is the size of a largest induced bipartite subgraph, +`λ(G) := max_v l(v)` is the maximum over all vertices of the independence +number of the open neighbourhood of `v`, and `dist_even(v)` is the number of +vertices at even distance from `v`. +-/ +@[category research solved, AMS 5] +theorem conjecture24 : answer(False) ↔ + ∀ {α : Type*} [Fintype α] [DecidableEq α] [Nontrivial α], + ∀ (G : SimpleGraph α) (_ : G.Connected), + let maxL := (Finset.univ.image (fun v => indepNeighborsCard G v)).max' (by simp) + let minDistEven := (Finset.univ.image (distEven G)).min' (by simp) + (maxL : ℝ) + ⌈(minDistEven : ℝ) / 3⌉ ≤ b G := by + sorry + +-- Sanity checks + +/-- `distEven G v` is always positive, since `v` itself is at distance 0 (even) from itself. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) (v : Fin 3) : 0 < distEven G v := by + unfold distEven + apply Finset.card_pos.mpr + exact ⟨v, Finset.mem_filter.mpr ⟨Finset.mem_univ _, ⟨0, by simp [SimpleGraph.dist_self]⟩⟩⟩ + +/-- The invariant `b G` is nonneg. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) : 0 ≤ b G := Nat.cast_nonneg _ + +end WrittenOnTheWallII.GraphConjecture24 diff --git a/FormalConjectures/WrittenOnTheWallII/GraphConjecture25.lean b/FormalConjectures/WrittenOnTheWallII/GraphConjecture25.lean new file mode 100644 index 000000000..37535638a --- /dev/null +++ b/FormalConjectures/WrittenOnTheWallII/GraphConjecture25.lean @@ -0,0 +1,75 @@ +/- +Copyright 2025 The Formal Conjectures Authors. + +Licensed under the Apache License, Version 2.0 (the "License"); +you may not use this file except in compliance with the License. +You may obtain a copy of the License at + + https://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, software +distributed under the License is distributed on an "AS IS" BASIS, +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +See the License for the specific language governing permissions and +limitations under the License. +-/ + +import FormalConjectures.Util.ProblemImports + +/-! +# Written on the Wall II - Conjecture 25 + +**Verbatim statement (WOWII #25, status F):** +> If G is a simple connected graph, then b(G) ≥ 2 CEIL[(1 + minimum of dist_even(v))/3] + +**Source:** http://cms.uhd.edu/faculty/delavinae/research/wowII/all.html#conj25 + +This conjecture is **disproved** on the WOWII page (status F; "same +counterexample as in #24"). Following the upstream pattern established in +#3823 for Conjecture 23, we record the disproof using `answer(False) ↔ ...`. + +*Reference:* +[E. DeLaVina, Written on the Wall II, Conjectures of Graffiti.pc](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) +-/ + +namespace WrittenOnTheWallII.GraphConjecture25 + +open Classical SimpleGraph + +/-- `distEven G v` counts the number of vertices at even distance from `v` in `G`. +Distance 0 (the vertex itself) is even, so `distEven G v ≥ 1`. -/ +noncomputable def distEven {α : Type*} [Fintype α] + (G : SimpleGraph α) (v : α) : ℕ := + (Finset.univ.filter (fun w => Even (G.dist v w))).card + +/-- +WOWII [Conjecture 25](http://cms.uhd.edu/faculty/delavinae/research/wowII/all.html#conj25) +(status F, disproved): + +For every finite simple connected graph `G`, +`b(G) ≥ 2 · ⌈(1 + min_v dist_even(v)) / 3⌉` +where `b(G)` is the size of a largest induced bipartite subgraph and +`dist_even(v)` is the number of vertices at even distance from `v`. +-/ +@[category research solved, AMS 5] +theorem conjecture25 : answer(False) ↔ + ∀ {α : Type*} [Fintype α] [DecidableEq α] [Nontrivial α], + ∀ (G : SimpleGraph α) (_ : G.Connected), + let minDistEven := (Finset.univ.image (distEven G)).min' (by simp) + 2 * ⌈(1 + (minDistEven : ℝ)) / 3⌉ ≤ b G := by + sorry + +-- Sanity checks + +/-- `distEven G v` is always at least 1, since `v` itself is at distance 0 (even) from itself. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 4)) (v : Fin 4) : 1 ≤ distEven G v := by + unfold distEven + apply Finset.card_pos.mpr + exact ⟨v, Finset.mem_filter.mpr ⟨Finset.mem_univ _, ⟨0, by simp [SimpleGraph.dist_self]⟩⟩⟩ + +/-- The invariant `b G` is nonneg. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) : 0 ≤ b G := Nat.cast_nonneg _ + +end WrittenOnTheWallII.GraphConjecture25 diff --git a/FormalConjectures/WrittenOnTheWallII/GraphConjecture63.lean b/FormalConjectures/WrittenOnTheWallII/GraphConjecture63.lean new file mode 100644 index 000000000..a25fc553c --- /dev/null +++ b/FormalConjectures/WrittenOnTheWallII/GraphConjecture63.lean @@ -0,0 +1,70 @@ +/- +Copyright 2025 The Formal Conjectures Authors. + +Licensed under the Apache License, Version 2.0 (the "License"); +you may not use this file except in compliance with the License. +You may obtain a copy of the License at + + https://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, software +distributed under the License is distributed on an "AS IS" BASIS, +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +See the License for the specific language governing permissions and +limitations under the License. +-/ + +import FormalConjectures.Util.ProblemImports + +/-! +# Written on the Wall II - Conjecture 63 + +**Verbatim statement (WOWII #63, status O):** +> If G is a simple connected graph, then f(G) ≥ CEIL[(minimum of dist_even(v) + b(G) + 1)/3] + +**Source:** http://cms.uhd.edu/faculty/delavinae/research/wowII/all.html#conj63 + + +*Reference:* +[E. DeLaVina, Written on the Wall II, Conjectures of Graffiti.pc](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) +-/ + +namespace WrittenOnTheWallII.GraphConjecture63 + +open Classical SimpleGraph + +variable {α : Type*} [Fintype α] [DecidableEq α] [Nontrivial α] + +/-- `distEven G v` counts the number of vertices at even distance from `v` in `G`. -/ +noncomputable def distEven (G : SimpleGraph α) (v : α) : ℕ := + (Finset.univ.filter (fun w => Even (G.dist v w))).card + +/-- +WOWII [Conjecture 63](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) + +For a simple connected graph `G`, +`f(G) ≥ ⌈(min_v distEven(v) + b(G) + 1) / 3⌉` +where `f(G) = largestInducedForestSize G` is the size of a largest induced forest, +`b(G)` is the largest induced bipartite subgraph size, and +`distEven(v)` is the number of vertices at even distance from `v`. +-/ +@[category research open, AMS 5] +theorem conjecture63 (G : SimpleGraph α) (h : G.Connected) : + let minDistEven := (Finset.univ.image (distEven G)).min' (by simp) + ⌈((minDistEven : ℝ) + b G + 1) / 3⌉ ≤ (G.largestInducedForestSize : ℝ) := by + sorry + +-- Sanity checks + +/-- The largest induced forest size is a natural number (nonneg). -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) : 0 ≤ G.largestInducedForestSize := Nat.zero_le _ + +/-- `distEven` of any vertex is positive. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) (v : Fin 3) : 0 < distEven G v := by + unfold distEven + apply Finset.card_pos.mpr + exact ⟨v, Finset.mem_filter.mpr ⟨Finset.mem_univ _, ⟨0, by simp [SimpleGraph.dist_self]⟩⟩⟩ + +end WrittenOnTheWallII.GraphConjecture63 diff --git a/FormalConjectures/WrittenOnTheWallII/GraphConjecture72.lean b/FormalConjectures/WrittenOnTheWallII/GraphConjecture72.lean new file mode 100644 index 000000000..86c27f474 --- /dev/null +++ b/FormalConjectures/WrittenOnTheWallII/GraphConjecture72.lean @@ -0,0 +1,75 @@ +/- +Copyright 2025 The Formal Conjectures Authors. + +Licensed under the Apache License, Version 2.0 (the "License"); +you may not use this file except in compliance with the License. +You may obtain a copy of the License at + + https://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, software +distributed under the License is distributed on an "AS IS" BASIS, +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +See the License for the specific language governing permissions and +limitations under the License. +-/ + +import FormalConjectures.Util.ProblemImports + +/-! +# Written on the Wall II - Conjecture 72 + +**Verbatim statement (WOWII #72, status O):** +> If G is a simple connected graph, then tree(G) ≥ CEIL[average of ecc(v) + maximum of λ(v) /3] + +**Source:** http://cms.uhd.edu/faculty/delavinae/research/wowII/all.html#conj72 + + +*Reference:* +[E. DeLaVina, Written on the Wall II, Conjectures of Graffiti.pc](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) +-/ + +namespace WrittenOnTheWallII.GraphConjecture72 + +open Classical SimpleGraph + +variable {α : Type*} [Fintype α] [DecidableEq α] [Nontrivial α] + +/-- `largestInducedTreeSize G` is the number of vertices in a largest induced subtree of `G`. +A tree is a connected acyclic graph; an induced tree is an induced subgraph that is a tree. -/ +noncomputable def largestInducedTreeSize (G : SimpleGraph α) : ℕ := + sSup { n | ∃ s : Finset α, s.card = n ∧ (G.induce (s : Set α)).IsTree } + +/-- The average eccentricity of `G`: the mean of `eccentricity G v` over all vertices. -/ +noncomputable def averageEccentricity (G : SimpleGraph α) : ℝ := + (∑ v : α, (G.eccentricity v).toNat) / (Fintype.card α : ℝ) + +/-- +WOWII [Conjecture 72](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) + +For a simple connected graph `G`, +`tree(G) ≥ ⌈(ecc_avg(G) + max_v l(v)) / 3⌉` +where `tree(G)` is the number of vertices in a largest induced tree, +`ecc_avg(G)` is the average eccentricity of `G`, and +`max_v l(v) = max_v indepNeighborsCard G v` is the maximum over all vertices of +the independence number of the neighbourhood. +-/ +@[category research open, AMS 5] +theorem conjecture72 (G : SimpleGraph α) (h : G.Connected) : + let maxL := (Finset.univ.image (fun v => indepNeighborsCard G v)).max' (by simp) + ⌈(averageEccentricity G + (maxL : ℝ)) / 3⌉ ≤ (largestInducedTreeSize G : ℝ) := by + sorry + +-- Sanity checks + +/-- The `largestInducedTreeSize` is nonneg. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) : 0 ≤ largestInducedTreeSize G := Nat.zero_le _ + +/-- The average eccentricity is nonneg. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) : 0 ≤ averageEccentricity G := by + unfold averageEccentricity + positivity + +end WrittenOnTheWallII.GraphConjecture72 diff --git a/FormalConjectures/WrittenOnTheWallII/GraphConjecture84.lean b/FormalConjectures/WrittenOnTheWallII/GraphConjecture84.lean new file mode 100644 index 000000000..d0fc44532 --- /dev/null +++ b/FormalConjectures/WrittenOnTheWallII/GraphConjecture84.lean @@ -0,0 +1,74 @@ +/- +Copyright 2025 The Formal Conjectures Authors. + +Licensed under the Apache License, Version 2.0 (the "License"); +you may not use this file except in compliance with the License. +You may obtain a copy of the License at + + https://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, software +distributed under the License is distributed on an "AS IS" BASIS, +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +See the License for the specific language governing permissions and +limitations under the License. +-/ + +import FormalConjectures.Util.ProblemImports + +/-! +# Written on the Wall II - Conjecture 84 + +**Verbatim statement (WOWII #84, status O):** +> If G is a simple connected graph, then tree(G) ≥ 2 rad(G) / δ(G) + +**Source:** http://cms.uhd.edu/faculty/delavinae/research/wowII/all.html#conj84 + +Here `δ(G)` is the **minimum degree** of `G` (lowercase delta in the WOWII +HTML, rendered as `d`), not the average distance. + +*Reference:* +[E. DeLaVina, Written on the Wall II, Conjectures of Graffiti.pc](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) +-/ + +namespace WrittenOnTheWallII.GraphConjecture84 + +open Classical SimpleGraph + +variable {α : Type*} [Fintype α] [DecidableEq α] [Nontrivial α] + +/-- `largestInducedTreeSize G` is the number of vertices in a largest induced subtree of `G`. -/ +noncomputable def largestInducedTreeSize (G : SimpleGraph α) : ℕ := + sSup { n | ∃ s : Finset α, s.card = n ∧ (G.induce (s : Set α)).IsTree } + +/-- +WOWII [Conjecture 84](http://cms.uhd.edu/faculty/delavinae/research/wowII/all.html#conj84) +(status O): + +For a simple connected graph `G` with positive minimum degree, +`tree(G) ≥ 2 · rad(G) / δ(G)`, +where `tree(G)` is the number of vertices in a largest induced subtree, +`rad(G)` is the radius, and `δ(G) = G.minDegree` is the minimum degree. + +The hypothesis `0 < G.minDegree` follows from connectedness on a nontrivial +vertex set, but is stated explicitly so the theorem reads as a real-valued +inequality without `x / 0` corner cases. +-/ +@[category research open, AMS 5] +theorem conjecture84 (G : SimpleGraph α) [DecidableRel G.Adj] + (h : G.Connected) (hδ : 0 < G.minDegree) : + 2 * (G.radius.toNat : ℝ) / (G.minDegree : ℝ) ≤ (largestInducedTreeSize G : ℝ) := by + sorry + +-- Sanity checks + +/-- The `largestInducedTreeSize` is nonneg. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) : 0 ≤ largestInducedTreeSize G := Nat.zero_le _ + +/-- The largest induced tree size is nonneg. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) : 0 ≤ (largestInducedTreeSize G : ℝ) := + Nat.cast_nonneg _ + +end WrittenOnTheWallII.GraphConjecture84 diff --git a/FormalConjectures/WrittenOnTheWallII/GraphConjecture85.lean b/FormalConjectures/WrittenOnTheWallII/GraphConjecture85.lean new file mode 100644 index 000000000..cb15220bb --- /dev/null +++ b/FormalConjectures/WrittenOnTheWallII/GraphConjecture85.lean @@ -0,0 +1,70 @@ +/- +Copyright 2025 The Formal Conjectures Authors. + +Licensed under the Apache License, Version 2.0 (the "License"); +you may not use this file except in compliance with the License. +You may obtain a copy of the License at + + https://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, software +distributed under the License is distributed on an "AS IS" BASIS, +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +See the License for the specific language governing permissions and +limitations under the License. +-/ + +import FormalConjectures.Util.ProblemImports + +/-! +# Written on the Wall II - Conjecture 85 + +**Verbatim statement (WOWII #85, status O):** +> If G is a simple connected graph, then tree(G) ≥ CEIL[sqrt(1 + 2*minimum of dist_even(v))] + +**Source:** http://cms.uhd.edu/faculty/delavinae/research/wowII/all.html#conj85 + + +*Reference:* +[E. DeLaVina, Written on the Wall II, Conjectures of Graffiti.pc](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) +-/ + +namespace WrittenOnTheWallII.GraphConjecture85 + +open Classical SimpleGraph + +variable {α : Type*} [Fintype α] [DecidableEq α] [Nontrivial α] + +/-- `distEven G v` counts the number of vertices at even distance from `v` in `G`. -/ +noncomputable def distEven (G : SimpleGraph α) (v : α) : ℕ := + (Finset.univ.filter (fun w => Even (G.dist v w))).card + +/-- `largestInducedTreeSize G` is the number of vertices in a largest induced subtree of `G`. -/ +noncomputable def largestInducedTreeSize (G : SimpleGraph α) : ℕ := + sSup { n | ∃ s : Finset α, s.card = n ∧ (G.induce (s : Set α)).IsTree } + +/-- +WOWII [Conjecture 85](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) + +For a simple connected graph `G`, +`tree(G) ≥ ⌈√(1 + 2 · min_v distEven(v))⌉` +where `tree(G)` is the number of vertices in a largest induced tree and +`distEven(v)` is the number of vertices at even distance from `v`. +-/ +@[category research open, AMS 5] +theorem conjecture85 (G : SimpleGraph α) (h : G.Connected) : + let minDistEven := (Finset.univ.image (distEven G)).min' (by simp) + ⌈Real.sqrt (1 + 2 * (minDistEven : ℝ))⌉ ≤ (largestInducedTreeSize G : ℝ) := by + sorry + +-- Sanity checks + +/-- The `largestInducedTreeSize` is nonneg. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) : 0 ≤ largestInducedTreeSize G := Nat.zero_le _ + +/-- `Real.sqrt` is nonneg. -/ +@[category test, AMS 5] +example (x : ℝ) : 0 ≤ Real.sqrt x := Real.sqrt_nonneg x + +end WrittenOnTheWallII.GraphConjecture85 diff --git a/FormalConjectures/WrittenOnTheWallII/GraphConjecture91.lean b/FormalConjectures/WrittenOnTheWallII/GraphConjecture91.lean new file mode 100644 index 000000000..aa83e1bc2 --- /dev/null +++ b/FormalConjectures/WrittenOnTheWallII/GraphConjecture91.lean @@ -0,0 +1,66 @@ +/- +Copyright 2025 The Formal Conjectures Authors. + +Licensed under the Apache License, Version 2.0 (the "License"); +you may not use this file except in compliance with the License. +You may obtain a copy of the License at + + https://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, software +distributed under the License is distributed on an "AS IS" BASIS, +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +See the License for the specific language governing permissions and +limitations under the License. +-/ + +import FormalConjectures.Util.ProblemImports + +/-! +# Written on the Wall II - Conjecture 91 + +**Verbatim statement (WOWII #91, status O):** +> If G is a simple connected graph, then b(G) ≤ 1 + f(G) * (CEIL[average of λ(v) ])/2 + +**Source:** http://cms.uhd.edu/faculty/delavinae/research/wowII/all.html#conj91 + + +*Reference:* +[E. DeLaVina, Written on the Wall II, Conjectures of Graffiti.pc](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) +-/ + +namespace WrittenOnTheWallII.GraphConjecture91 + +open Classical SimpleGraph + +variable {α : Type*} [Fintype α] [DecidableEq α] [Nontrivial α] + +/-- +WOWII [Conjecture 91](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) + +For a simple connected graph `G`, +`b(G) ≤ 1 + f(G) · ⌈avg_v l(v)⌉ / 2` +where `b(G)` is the largest induced bipartite subgraph size, +`f(G) = largestInducedForestSize G` is the largest induced forest size, and +`avg_v l(v) = l G` is the average independence number of the neighbourhoods. +-/ +@[category research open, AMS 5] +theorem conjecture91 (G : SimpleGraph α) (h : G.Connected) : + b G ≤ 1 + (G.largestInducedForestSize : ℝ) * ⌈l G⌉ / 2 := by + sorry + +-- Sanity checks + +/-- The invariant `b G` is nonneg. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) : 0 ≤ b G := Nat.cast_nonneg _ + +/-- The average indep-neighbors `l G` is nonneg. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) : 0 ≤ l G := by + unfold l averageIndepNeighbors + apply div_nonneg + · apply Finset.sum_nonneg; intro v _; exact Nat.cast_nonneg _ + · exact Nat.cast_nonneg _ + +end WrittenOnTheWallII.GraphConjecture91 diff --git a/FormalConjectures/WrittenOnTheWallII/GraphConjecture96.lean b/FormalConjectures/WrittenOnTheWallII/GraphConjecture96.lean new file mode 100644 index 000000000..63cb0d7c6 --- /dev/null +++ b/FormalConjectures/WrittenOnTheWallII/GraphConjecture96.lean @@ -0,0 +1,68 @@ +/- +Copyright 2025 The Formal Conjectures Authors. + +Licensed under the Apache License, Version 2.0 (the "License"); +you may not use this file except in compliance with the License. +You may obtain a copy of the License at + + https://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, software +distributed under the License is distributed on an "AS IS" BASIS, +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +See the License for the specific language governing permissions and +limitations under the License. +-/ + +import FormalConjectures.Util.ProblemImports + +/-! +# Written on the Wall II - Conjecture 96 + +**Verbatim statement (WOWII #96, status O):** +> If G is a simple connected graph, then α(G) ≤ 1 + minimum dist_even(v)*(maximum of λ(v) -1) + +**Source:** http://cms.uhd.edu/faculty/delavinae/research/wowII/all.html#conj96 + + +*Reference:* +[E. DeLaVina, Written on the Wall II, Conjectures of Graffiti.pc](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) +-/ + +namespace WrittenOnTheWallII.GraphConjecture96 + +open Classical SimpleGraph + +variable {α : Type*} [Fintype α] [DecidableEq α] [Nontrivial α] + +/-- `distEven G v` counts the number of vertices at even distance from `v` in `G`. -/ +noncomputable def distEven (G : SimpleGraph α) (v : α) : ℕ := + (Finset.univ.filter (fun w => Even (G.dist v w))).card + +/-- +WOWII [Conjecture 96](http://cms.dt.uh.edu/faculty/delavinae/research/wowII/) + +For a simple connected graph `G`, +`α(G) ≤ 1 + min_v distEven(v) · (max_v l(v) - 1)` +where `α(G) = G.indepNum` is the independence number, +`distEven(v)` is the number of vertices at even distance from `v`, and +`max_v l(v)` is the maximum independence number of a vertex neighbourhood. +-/ +@[category research open, AMS 5] +theorem conjecture96 (G : SimpleGraph α) (h : G.Connected) : + let minDistEven := (Finset.univ.image (distEven G)).min' (by simp) + let maxL := (Finset.univ.image (fun v => indepNeighborsCard G v)).max' (by simp) + (G.indepNum : ℝ) ≤ 1 + (minDistEven : ℝ) * ((maxL : ℝ) - 1) := by + sorry + +-- Sanity checks + +/-- The independence number is nonneg. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) : 0 ≤ G.indepNum := Nat.zero_le _ + +/-- The independence number is nonneg. -/ +@[category test, AMS 5] +example (G : SimpleGraph (Fin 3)) : 0 ≤ G.indepNum := Nat.zero_le _ + +end WrittenOnTheWallII.GraphConjecture96