EriksonStage
plain-language theorem explainer
EriksonStage enumerates the eight psychosocial stages as an inductive type with decidable equality and Fintype structure. Researchers modeling dementia as reversal of developmental order would cite this enumeration when certifying the 2^3 cycle and involution on Fin 8. The declaration is a direct inductive enumeration that derives the required typeclass instances with no additional proof steps.
Claim. Let $E$ be the inductive type whose constructors are the eight stages trust versus mistrust, autonomy versus shame, initiative versus guilt, industry versus inferiority, identity versus confusion, intimacy versus isolation, generativity versus stagnation, and integrity versus despair. The type $E$ carries decidable equality and is finite of cardinality 8.
background
The module states that Erikson's eight life stages form a 2^3 tick cycle and that neurodegeneration traverses the ladder in reverse order. The reversal operation is the order-reversing involution on Fin 8 given by reverse k = 7 - k. This inductive type supplies the concrete enumeration of stages required to state and certify those structural properties.
proof idea
The declaration is the inductive definition itself. It lists the eight constructors explicitly and lets Lean derive the DecidableEq, Repr, BEq, and Fintype instances automatically.
why it matters
EriksonStage is the base enumeration used by DevelopmentReversalCert to assert cardinality 8, equality to 2^3, involution of the reverse map, and the midlife-first inversion property. It realizes the eight-tick octave (T7) of the Recognition Science forcing chain inside the cross-domain reversal model. The definition closes the structural scaffolding for the predicted clinical pattern of dementia progression.
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