EDB — 1WC

[1WC] Explain the formula \(⋃_{B∈{\mathcal P}(A)} B\) using the definition [1Y2]↺↻ of the axiom of union. Then show that \(A=⋃_{B∈{\mathcal P}(A)} B\).

See also [028]↺↻ where the same result is obtained starting from the axiom of union as defined in [026]↺↻ in the Zermelo–Fraenkel axiomatic.