erikson_eq_2cube
plain-language theorem explainer
The theorem fixes the cardinality of the Erikson stages at exactly eight. Modelers of neurodegeneration reversal cite it to anchor the 2^3 tick cycle before defining the order-reversing involution. The proof is a one-line decision procedure that evaluates the derived Fintype instance on the eight-constructor inductive type.
Claim. Let $E$ be the finite type whose elements are the eight Erikson stages. Then $|E| = 2^3$.
background
The module formalizes C6: Development Reversal as an involution on a 2^3 cycle of life stages. EriksonStage is the inductive type with constructors trustVsMistrust through integrityVsDespair, deriving Fintype so that its cardinality is computable by decision procedures. The local setting treats the stages as an eight-tick octave whose reversal map is order-reversing on Fin 8.
proof idea
One-line wrapper that applies the decide tactic to Fintype.card on the inductive type EriksonStage.
why it matters
The result supplies the stage_count and two_cube fields of developmentReversalCert. It realizes the T7 eight-tick octave landmark inside the cross-domain reversal claim. The certificate then chains this cardinality to the involution and endpoint-swap properties.
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