theorem
proved
term proof
reverse_swaps_endpoints
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formal statement (Lean)
44theorem reverse_swaps_endpoints :
45 reverse ⟨0, by decide⟩ = ⟨7, by decide⟩ ∧
46 reverse ⟨7, by decide⟩ = ⟨0, by decide⟩ := by
proof body
Term-mode proof.
47 refine ⟨?_, ?_⟩
48 · apply Fin.ext; simp [reverse]
49 · apply Fin.ext; simp [reverse]
50
51/-- Mid-life stages invert before early ones:
52 reverse of stage 6 (generativity) = stage 1 (autonomy),
53 reverse of stage 0 (trust) = stage 7 (integrity).
54 So going in reverse from old-age, we pass stage 6's inverse at
55 position 1 before stage 0's inverse at position 7. -/