The many faces of circle orders
Tóm tắt
A finite partially ordered set P is called a circle order if one can assign to each x ∈ P a circular disk C
x
so that x≤y iff C
x
$$ \subseteq $$
C
y
. It is interesting to observe that many other classes of posets, such as space-time orders, parabola orders, the Loewner order for 2×2 Hermitian matrices, etc. turn out to be exactly circle orders (or their higher dimensional analogues). We give a “global” proof for these equivalences.
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