x1 is the traditional/standard/classical strict total-order(ing) '<' which endows the (extended) real numbers.
This is the order by which -\infty (infty) < r < +\infty (infty) for all r in the reals, \dots < -2 < -1 < 0 < +1 < +2 < \dots, 0 < r1/q < r for all r1, r in the naturals such that r1 < r, etc. Occasionally isomorphically intersects cleispoi and moinspoi. See also: enspoi.