In 2020, Scott Aaronson conjectured that the busy beaver function of 20 was the upper bound of what this system could prove. (-5[1])Shelah showed (10[1])that two implications of this system (10[1])produce contradictory answers to the Whitehead problem. (10[1])The first-order form (10[1])of this system violates the Löwenheim–Skolem (-5[1])theorem, (-5[2])leading to Skolem’s (10[1])paradox. (10[2])In 1963, Paul Cohen used forcing (10[1]-5[1])to show (10[1])that this system (10[5])and the continuum (10[1])hypothesis (10[4])are independent (10[1])of each other. (10[5])This (10[1])system’s (10[3])inclusion (10[1])of (10[1])the axiom of specification (10[2])allows (10[1])it to avoid (10[1]-5[1])Russell’s paradox. (10[2]-5[1])The letter (-5[1])C (-5[1])is appended (10[1])to this (10[1])system’s (10[1])name (10[2])to indicate (10[2])its inclusion (10[1])of the axiom (10[1])of (10[1])choice. (10[1])For 10 points, (10[1])name this standard formulation of set theory (10[2])proposed (10[1])by two German mathematicians, (10[1])often (10[1])known (10[1])by a two-letter (10[2])acronym. (10[1]) (10[5]0[24])■END■