Zulip Chat Archive
Stream: new members
Topic: A version of add_le_add for indexed sums
Ryan Smith (Sep 03 2025 at 18:55):
I have been trying to find this result with leanexplore and moogle but without luck:
I have a finite set s of complex numbers and for each z \in s I have an inequality |z| \le |w|. Isn't there a version of add_le_add for an indexed sum?
∑ z ∈ s, ‖z‖ \le ∑ z ∈ s, ‖w‖
Eric Wieser (Sep 03 2025 at 18:55):
@loogle "sum_le_sum"
loogle (Sep 03 2025 at 18:55):
:search: List.Forall₂.sum_le_sum, List.sum_le_sum, and 22 more
Eric Wieser (Sep 03 2025 at 18:56):
From that list, docs#Finset.sum_le_sum is what you want
Eric Wieser (Sep 03 2025 at 18:57):
A better query would have been
@loogle: ∑ z ∈ ?s, _ ≤ ∑ z ∈ ?s, _
loogle (Sep 03 2025 at 18:57):
:search: Finset.sum_le_sum, Finset.exists_le_of_sum_le, and 19 more
Ryan Smith (Sep 03 2025 at 20:23):
Thanks, I need to get comfortable with loogle since it seems quite powerful for finding results.
Last updated: Dec 20 2025 at 21:32 UTC