English
If a function is Multipliable with respect to a larger filter L2 and L1's filter is contained in L2's, then the same function is Multipliable with respect to L1.
Русский
Если f суммируемо по L2, и фильтр L1 подпадает под L2, то f суммируемо по L1.
LaTeX
$$$ Multipliable f L_2 \rightarrow (L_1.filter \le L_2.filter) \rightarrow Multipliable f L_1 $$$
Lean4
@[to_additive]
theorem mono_filter {f : β → α} {L₁ L₂ : SummationFilter β} (hf : Multipliable f L₂) (h : L₁.filter ≤ L₂.filter) :
Multipliable f L₁ :=
match hf with
| ⟨a, ha⟩ => ⟨a, ha.mono_left h⟩