Description: This theorem expresses two different facts from the two subset implications in this equality. In the forward direction, it says that the transitive closure has members of every rank below A . Stated another way, to construct a set at a given rank, you have to climb the entire hierarchy of ordinals below ( rankA ) , constructing at least one set at each level in order to move up the ranks. In the reverse direction, it says that every member of ( TCA ) has a rank below the rank of A , since intuitively it contains only the members of A and the members of those and so on, but nothing "bigger" than A . (Contributed by Mario Carneiro, 23-Jun-2013)
Ref | Expression | ||
---|---|---|---|
Assertion | tcrank | |