convert Finset.sum_sdiff (s₁ := Finset.Ioc b c) (s₂ := Finset.Ioc a c) ?_
a b c : ℤ
f : ℤ → ℂ
hb : b ∈ Icc a c
⊢ ∑ n ∈ Ioc a b, f n + ∑ n ∈ Ioc b c, f n = ∑ n ∈ Ioc a c, f n
case h.e'_2.h.e'_5.h
a b c : ℤ
f : ℤ → ℂ
hb : b ∈ Icc a c
⊢ Ioc a b = Ioc a c \ Ioc b c

case convert_4
a b c : ℤ
f : ℤ → ℂ
hb : b ∈ Icc a c
⊢ Ioc b c ⊆ Ioc a c