# What is the term for saying something like A is B,and B is A?

Watching an ad about a mobile network operator that recently changed it's brand name:
Tunisiana is ooredooo, and ooredoo is Tunisiana

is there a term for this kind of statement?
another example: One for all, and all for one

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"Fair is foul, and foul is fair." (William Shakespeare, Macbeth I.i) – Kris Apr 25 '14 at 9:28

Chiasmus is the classical term for examples of 'cross-over phrasing'.

How 'classical'

Nice to see you ... to see you, nice.

was is another matter.

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+1 for Brucie :) – oerkelens Apr 25 '14 at 8:52

Mathematically, the statement "A is B and B is A" postulates an equivalence of A and B, i.e. that they can be used interchangeably (as opposed to one being a subset of the other).

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But that doesn't hold for the second example :) – oerkelens Apr 25 '14 at 9:01
Mathematically, the statement "A R B <=> B R A" defines merely the symmetry aspect of a possible equivalence relation on a set containing (general) elements A and B. The relation R can of course be 'equals' / 'is [the same as]'. "A is/equals B" is enough to specify an equivalence relation in this case. Reflexivity (eg, where the relation is 'equals', A = A) and transitivity (A = B and B = C => A = C) are also required properties. – Edwin Ashworth Apr 25 '14 at 9:18
@EdwinAshworth To me this type of sentence rather describes a reciprocity. You say A R B (`=>` ie. necessary condition) , but then also B R A (`<=` aka. satisfying condition). – Pierre Arlaud Apr 25 '14 at 12:18
@ Arlaud Pierre I'm sorry, which type of sentence? A symmetric relation, say ~, is one where if a ~ b then b ~ a for all a,b within the set / population. Obviously, 'is greater than' is not a symmetric relation (and hence not an equivalence relation), because a > b does not permit b > a. [But this is maths. I'm pointing out here that this answer is perhaps unhelpful. As does oerkelens. And 'reciprocity relation' has a different, defined meaning in calculus.] – Edwin Ashworth Apr 25 '14 at 15:02