The wikipedia article on Paul Cohen mentions that:
Cohen is noted for developing a mathematical technique called forcing, which he used to prove that neither the continuum hypothesis (CH), nor the axiom of choice, can be proved from the standard Zermelo–Fraenkel axioms (ZF) of set theory.
I am trying to find out the exact year in which Coehn first proved the result concerning the axiom of choice and the year and the paper when it was first published, if ever. All I have found are two papers related to this. (See here and here.) However both of these relate to the independence of the continuum hypothesis and not of the axiom of choice. My precise questions are in which year did Cohen prove the result concerning the axiom of choice, and when was it first published or presented?