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def definition def or abbrev

neg

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 114def neg : LogicInt → LogicInt :=

proof body

Definition body.

 115  Quotient.lift (fun (p : LogicNat × LogicNat) => mk p.2 p.1) (by
 116    rintro ⟨a, b⟩ ⟨c, d⟩ h
 117    show mk b a = mk d c
 118    apply sound
 119    show b + c = d + a
 120    rw [eq_iff_toNat_eq, toNat_add, toNat_add]
 121    have h' : toNat a + toNat d = toNat c + toNat b := by
 122      have := congrArg toNat (show a + d = c + b from h)
 123      rwa [toNat_add, toNat_add] at this
 124    omega)
 125
 126instance : Neg LogicInt := ⟨neg⟩
 127
 128/-- Addition: `(a, b) + (c, d) = (a + c, b + d)`. -/

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