English
The limsup of a function along a filter equals the infimum of the sInf set of upper bounds of the tail behavior of the function under the map u.
Русский
Предел верхний по функции и фильтру равен инфимума множества верхних граней хвостового поведения функции под отображением u.
LaTeX
$$$\operatorname{limsup} u f = \inf\{a : \text{eventually } u \le a\}$$$
Lean4
/-- The `limsInf` of a filter `f` is the supremum of the `a` such that the inequality
`x ≥ a` eventually holds for `f`. -/
def limsInf (f : Filter α) : α :=
sSup {a | ∀ᶠ n in f, a ≤ n}