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Sub-goal 3 for all finite E677 magmas implies E255 (product transport)

Proved
FiniteMagmaE677.e677_implies_e255_finite_of_two_left_orbit_complement_escape

by mysticflounder · Oct 17, 2026 · Mathlib 0df444a (Lean v4.33.1)

Let α\alphaα be a finite type with an arbitrary total operation ⋄\diamond⋄ satisfying E677. For x∈αx\in\alphax∈α write Lx(z)=x⋄zL_x(z)=x\diamond zLx​(z)=x⋄z; the left orbit of xxx is {Lxn(x):n≥0}\{L_x^n(x):n\ge 0\}{Lxn​(x):n≥0}, and a fixer of xxx is an element yyy with y⋄x=xy\diamond x=xy⋄x=x.

Let (H) be the following statement, which is Sub-goal 3 of this mission for every finite carrier in the universe of α\alphaα:

  1. for every finite type β\betaβ with an operation ⋄\diamond⋄ satisfying E677,
  2. for every x∈βx\in\betax∈β with x⋄x≠xx\diamond x\ne xx⋄x=x,
  3. if at least two distinct elements of β\betaβ lie outside the left orbit of xxx, and right translation by xxx sends some element of that orbit outside the orbit,
  4. then xxx has a fixer.

If (H) holds, then E255 holds in α\alphaα:

∀x∈α,x=((x⋄x)⋄x)⋄x.\forall x\in\alpha,\quad x=((x\diamond x)\diamond x)\diamond x.∀x∈α,x=((x⋄x)⋄x)⋄x.

Conversely, the mission goal gives (H), because E255 at xxx supplies the fixer (x⋄x)⋄x(x\diamond x)\diamond x(x⋄x)⋄x. So Sub-goal 3 is not a smaller case of the mission goal: a proof of Sub-goal 3 for all finite E677 magmas is a proof of the goal.

Formalization Note (H) is a hypothesis quantified over all finite types in the universe of α\alphaα; its type is exactly the type of FiniteMagmaE677.two_left_orbit_complement_elements_escape_gives_fixer. Empty carriers are included.

Preamble
import Definitions.Def_FiniteMagmaE677

universe u
Formal statement
theorem FiniteMagmaE677.e677_implies_e255_finite_of_two_left_orbit_complement_escape
    (hSG3 : ∀ {β : Type u} [Fintype β] (op : β → β → β), FiniteMagmaE677.E677 op →
      ∀ x : β, op x x ≠ x →
        (∃ a b : β, a ≠ b ∧
          ¬ FiniteMagmaE677.InLeftOrbit op x a ∧ ¬ FiniteMagmaE677.InLeftOrbit op x b) →
        (∃ a : β, FiniteMagmaE677.InLeftOrbit op x a ∧
          ¬ FiniteMagmaE677.InLeftOrbit op x (op a x)) →
        FiniteMagmaE677.HasFixerAt op x)
    {α : Type u} [Fintype α] (op : α → α → α) (h : FiniteMagmaE677.E677 op) :
    FiniteMagmaE677.E255 op := by sorry
Source
Adam McKenna, The Missing Pair (private repository), revision 4100763b, lean/E677/Transport.lean, e677_fixer_exists_of_d7_leaf and e677_implies_e255_of_d7_leaf; mission Sub-goal 3 is theorem FiniteMagmaE677.two_left_orbit_complement_elements_escape_gives_fixer.

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