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The Dimension of a Poset  is the size of the smallest Realizer of
 is the size of the smallest Realizer of  . Equivalently, it
is the smallest Integer
. Equivalently, it
is the smallest Integer  such that
 such that  is Isomorphic to a Dominance order in
 is Isomorphic to a Dominance order in
 .
.
See also Dimension, Dominance, Isomorphic Posets, Realizer
References
Dushnik, B. and Miller, E. W.  ``Partially Ordered Sets.''  Amer. J. Math. 63, 600-610, 1941.
 
Trotter, W. T.  Combinatorics and Partially Ordered Sets: Dimension Theory.
  Baltimore, MD: Johns Hopkins University Press, 1992.