intro (rn//rd)
ℕ : Type
inst✝¹ : Natural ℕ
ℤ : Type
inst✝ : Integer ℤ
pn pd : ℤ
denominator_positive✝¹ : Logic.AP (Positive pd)
qn qd : ℤ
denominator_positive✝ : Logic.AP (Positive qd)
⊢ ∀ {r : Fraction ℤ}, pn//pd + qn//qd + r ≃ pn//pd + (qn//qd + r)
ℕ : Type
inst✝¹ : Natural ℕ
ℤ : Type
inst✝ : Integer ℤ
pn pd : ℤ
denominator_positive✝² : Logic.AP (Positive pd)
qn qd : ℤ
denominator_positive✝¹ : Logic.AP (Positive qd)
rn rd : ℤ
denominator_positive✝ : Logic.AP (Positive rd)
⊢ pn//pd + qn//qd + rn//rd ≃ pn//pd + (qn//qd + rn//rd)