Zulip Chat Archive

Stream: maths

Topic: When does order topology coincide with the norm topology?


Yongxi Lin (Aaron) (Feb 03 2026 at 12:48):

In #34770, I proved that the optional stopping theorem is true for a submartingale taking values in a type E such that

[NormedAddCommGroup E] [NormedSpace ℝ E] [CompleteSpace E]
[LinearOrder E] [OrderTopology E] [HasSolidNorm E] [SecondCountableTopology E] [IsOrderedAddMonoid E] [IsStrictOrderedModule ℝ E]

I start to worry whether this is really meaningful, as I can't think of a nontrivial example (i.e. E ≠ ℝ) such that E satisfies all these properties. Are there any references that can help me 1. find out related (counter)examples 2.better understand the interplay between orders and norms?

Sébastien Gouëzel (Feb 03 2026 at 13:05):

There is just R\R and 0{0}. If your space is a linear order with the order topology, then all points (but at most two) should be cut-points, i.e., E \ {x} should not be connected. But on a real vector space with dimension at least 2, then E \ {x} is connected. So your space should have dimension 0 or 1.

Yongxi Lin (Aaron) (Feb 04 2026 at 19:09):

You are right, so indeed I didn't prove anything new...I'll modify my PR


Last updated: Feb 28 2026 at 14:05 UTC