rw [x_from_coe, h]
case this
a b c z : ℤα
h : OneHom.toFun (↑↑inclusion) z = 0
⊢ ↑z.z = 0

case mp.z
a b c z : ℤα
h : OneHom.toFun (↑↑inclusion) z = 0
this : ↑z.z = 0
⊢ z.z = 0.z
case this
a b c z : ℤα
h : OneHom.toFun (↑↑inclusion) z = 0
⊢ 0.re - rt7⁻¹ * 0.im = 0

case mp.z
a b c z : ℤα
h : OneHom.toFun (↑↑inclusion) z = 0
this : ↑z.z = 0
⊢ z.z = 0.z