English
In a coatomic lattice α, if a ⊔ radical(α) = ⊤, then a = ⊤.
Русский
В коатомной решётке α, если a ⊔ radical(α) = ⊤, то a = ⊤.
LaTeX
$$$\text{In a coatomic lattice } \alpha:\ a \lor \operatorname{radical}(\alpha) = \top \Rightarrow a = \top.$$$
Lean4
theorem map_radical (f : α ≃o β) : f (Order.radical α) = Order.radical β :=
by
unfold Order.radical
simp only [OrderIso.map_iInf]
fapply Equiv.iInf_congr
· exact f.toEquiv
· simp