lemma proved term proof

`phi_approx`

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formal statement (Lean)

 507lemma phi_approx : phi < (1.62 : ℝ) := phi_lt_onePointSixTwo

Term-mode proof.

 508
 509/-- J(φ) = φ - 3/2 (exact, using φ² = φ + 1). -/

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