The result stated in the title is proved in this note. Actually we show that S x N is not a circle order, where S = {(1, 1), (1, 2), (1, 3), (2, 1), (2, 3)}. Furthermore this non-circle order is critical in the sense that (S - {x}) x N is a circle order for any x in S.
關聯:
ORDER-A JOURNAL ON THE THEORY OF ORDERED SETS AND ITS APPLICATIONS
