set.props.id(prop)

Defines the property name on items that uniquely identifies them. This is the default sorted property if no sort is provided.

var algebra = new set.Algebra(set.props.id("_id"));
algebra.index(
  {sortBy: "name desc"},
  [{name: "Meyer"}],
  {name: "Adams"}) //-> 1

algebra.index(
  {sortBy: "name"},
  [{name: "Meyer"}],
  {name: "Adams"}) //-> 0