# Talk:Maximally stable extremal regions

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## unintelligible formula

Hi, In this article, I have an objection to using the formula ${\displaystyle q(i)=|Q_{i+\Delta }\setminus Q_{i-\Delta }|/|Q_{i}|}$.
I know it's in the paper by Matas but as all Q are sets, I have no idea what the operator / is supposed to mean. If this is not simply due to my lack of mathematical understanding, it would be good to clarify what is meant by this expression. —Preceding unsigned comment added by 138.246.7.32 (talk) 11:34, 10 February 2010 (UTC)

I don't agree that the division symbol needs explaining. However, perhaps you have misunderstood what is here. The pipes |.|, which denote cardinality, turn the sets into normal real numbers. Thus, the division sign is then just a normal division. If anything, perhaps the |.| needs to be explained. Blackshadowshade (talk) 16:01, 7 May 2010 (UTC)

Perhaps $q(i) = \frac{| Q_{i+\Delta} \setminus Q_{i-\Delta} |}{|Q_i|}$ would be clearer?

${\displaystyle q(i)={\frac {|Q_{i+\Delta }\setminus Q_{i-\Delta }|}{|Q_{i}|}}}$

50.80.100.93 (talk) 04:58, 9 February 2016 (UTC)

## dead link

Just noticed that reference #3 returns a "Forbidden" error, is there another source available? —Preceding unsigned comment added by 38.110.4.86 (talk) 03:17, 24 January 2011 (UTC)

## Misleading definition of totally ordered set

According to https://en.wikipedia.org/wiki/Total_order , totally ordered set is a set X that has relation, that is antisymmetric, transitive and total. With the given definition without totality (antisymmetric, transitive, reflexive), there can be pairs of different elements from X that are not related to each other. Totality implies reflexivity.