In the study of these obj
In the study of these objects, the technique of forcing can be used to prove independence, while one theorem states that any of these can be given a well-ordering. One statement about these says that the Cartesian product of non-empty ones is non-empty, and the "power" one of these has higher cardinality than the underlying one of these. One named after Cantor is formed by recursively removing the middle thirds of intervals, and they often are studied using Zermelo-Frankel axioms, which do not include the axiom of choice. For 10 points, identify these mathematical objects which can be combined using unions and intersections and are collections of distinct objects.
In the study of these objects, the technique of forcing can be used to prove independence, while one theorem states that any of these can be given a well-ordering.