Theorem: Hindman.exists_FS_of_large
File: Mathlib/Combinatorics/Hindman.lean

Proof steps:
state_before: M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
s₀ : Set M
sU : s₀ ∈ U
⊢ ∃ a, FP a ⊆ s₀
state_after: M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
s₀ : Set M
sU : s₀ ∈ U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
⊢ ∃ a, FP a ⊆ s₀
tactic: have exists_elem : ∀ {s : Set M} (_hs : s ∈ U), (s ∩ { m | ∀ᶠ m' in U, m * m' ∈ s }).Nonempty :=
    fun {s} hs => Ultrafilter.nonempty_of_mem (inter_mem hs <| by rwa [← U_idem] at hs)
state_before: M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
s₀ : Set M
sU : s₀ ∈ U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
⊢ ∃ a, FP a ⊆ s₀
state_after: M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
s₀ : Set M
sU : s₀ ∈ U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
⊢ ∃ a, FP a ⊆ s₀
tactic: let elem : { s // s ∈ U } → M := fun p => (exists_elem p.property).some
state_before: M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
s₀ : Set M
sU : s₀ ∈ U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
⊢ ∃ a, FP a ⊆ s₀
state_after: M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
s₀ : Set M
sU : s₀ ∈ U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
succ : { s // s ∈ U } → { s // s ∈ U } := fun p => ⟨↑p ∩ {m | elem p * m ∈ ↑p}, ⋯⟩
⊢ ∃ a, FP a ⊆ s₀
tactic: let succ : {s // s ∈ U} → {s // s ∈ U} := fun (p : {s // s ∈ U}) =>
        ⟨p.val ∩ {m : M | elem p * m ∈ p.val},
         inter_mem p.property
           (show (exists_elem p.property).some ∈ {m : M | ∀ᶠ (m' : M) in ↑U, m * m' ∈ p.val} from
              p.val.inter_subset_right (exists_elem p.property).some_mem)⟩
state_before: M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
s₀ : Set M
sU : s₀ ∈ U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
succ : { s // s ∈ U } → { s // s ∈ U } := fun p => ⟨↑p ∩ {m | elem p * m ∈ ↑p}, ⋯⟩
⊢ ∃ a, FP a ⊆ s₀
state_after: case h
M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
s₀ : Set M
sU : s₀ ∈ U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
succ : { s // s ∈ U } → { s // s ∈ U } := fun p => ⟨↑p ∩ {m | elem p * m ∈ ↑p}, ⋯⟩
⊢ FP (Stream'.corec elem succ ⟨s₀, sU⟩) ⊆ s₀
tactic: use Stream'.corec elem succ (Subtype.mk s₀ sU)
state_before: case h
M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
s₀ : Set M
sU : s₀ ∈ U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
succ : { s // s ∈ U } → { s // s ∈ U } := fun p => ⟨↑p ∩ {m | elem p * m ∈ ↑p}, ⋯⟩
⊢ FP (Stream'.corec elem succ ⟨s₀, sU⟩) ⊆ s₀
state_after: case h
M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
s₀ : Set M
sU : s₀ ∈ U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
succ : { s // s ∈ U } → { s // s ∈ U } := fun p => ⟨↑p ∩ {m | elem p * m ∈ ↑p}, ⋯⟩
⊢ ∀ (a : Stream' M), ∀ m ∈ FP a, ∀ (p : { s // s ∈ U }), a = Stream'.corec elem succ p → m ∈ ↑p
tactic: suffices ∀ (a : Stream' M), ∀ m ∈ FP a, ∀ p, a = Stream'.corec elem succ p → m ∈ p.val by
    intro m hm
    exact this _ m hm ⟨s₀, sU⟩ rfl
state_before: case h
M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
s₀ : Set M
sU : s₀ ∈ U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
succ : { s // s ∈ U } → { s // s ∈ U } := fun p => ⟨↑p ∩ {m | elem p * m ∈ ↑p}, ⋯⟩
⊢ ∀ (a : Stream' M), ∀ m ∈ FP a, ∀ (p : { s // s ∈ U }), a = Stream'.corec elem succ p → m ∈ ↑p
state_after: case h
M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
succ : { s // s ∈ U } → { s // s ∈ U } := fun p => ⟨↑p ∩ {m | elem p * m ∈ ↑p}, ⋯⟩
⊢ ∀ (a : Stream' M), ∀ m ∈ FP a, ∀ (p : { s // s ∈ U }), a = Stream'.corec elem succ p → m ∈ ↑p
tactic: clear sU s₀
state_before: case h
M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
succ : { s // s ∈ U } → { s // s ∈ U } := fun p => ⟨↑p ∩ {m | elem p * m ∈ ↑p}, ⋯⟩
⊢ ∀ (a : Stream' M), ∀ m ∈ FP a, ∀ (p : { s // s ∈ U }), a = Stream'.corec elem succ p → m ∈ ↑p
state_after: case h
M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
succ : { s // s ∈ U } → { s // s ∈ U } := fun p => ⟨↑p ∩ {m | elem p * m ∈ ↑p}, ⋯⟩
a : Stream' M
m : M
h : m ∈ FP a
⊢ ∀ (p : { s // s ∈ U }), a = Stream'.corec elem succ p → m ∈ ↑p
tactic: intro a m h
state_before: case h
M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
succ : { s // s ∈ U } → { s // s ∈ U } := fun p => ⟨↑p ∩ {m | elem p * m ∈ ↑p}, ⋯⟩
a : Stream' M
m : M
h : m ∈ FP a
⊢ ∀ (p : { s // s ∈ U }), a = Stream'.corec elem succ p → m ∈ ↑p
state_after: case h.head
M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
succ : { s // s ∈ U } → { s // s ∈ U } := fun p => ⟨↑p ∩ {m | elem p * m ∈ ↑p}, ⋯⟩
a : Stream' M
m : M
b : Stream' M
⊢ ∀ (p : { s // s ∈ U }), b = Stream'.corec elem succ p → b.head ∈ ↑p

case h.tail
M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
succ : { s // s ∈ U } → { s // s ∈ U } := fun p => ⟨↑p ∩ {m | elem p * m ∈ ↑p}, ⋯⟩
a : Stream' M
m : M
b : Stream' M
n : M
h : FP b.tail n
ih : ∀ (p : { s // s ∈ U }), b.tail = Stream'.corec elem succ p → n ∈ ↑p
⊢ ∀ (p : { s // s ∈ U }), b = Stream'.corec elem succ p → n ∈ ↑p

case h.cons
M : Type u_1
inst✝ : Semigroup M
U : Ultrafilter M
U_idem : U * U = U
exists_elem : ∀ {s : Set M}, s ∈ U → (s ∩ {m | ∀ᶠ (m' : M) in ↑U, m * m' ∈ s}).Nonempty
elem : { s // s ∈ U } → M := fun p => ⋯.some
succ : { s // s ∈ U } → { s // s ∈ U } := fun p => ⟨↑p ∩ {m | elem p * m ∈ ↑p}, ⋯⟩
a : Stream' M
m : M
b : Stream' M
n : M
h : FP b.tail n
ih : ∀ (p : { s // s ∈ U }), b.tail = Stream'.corec elem succ p → n ∈ ↑p
⊢ ∀ (p : { s // s ∈ U }), b = Stream'.corec elem succ p → b.head * n ∈ ↑p
tactic: induction' h with b b n h ih b n h ih