We have the following indirect implication of form equivalence classes:
			
| Implication | Reference | 
|---|---|
| 50 \(\Rightarrow\) 14 | A survey of recent results in set theory, Mathias,  A.R.D. 1979, Period. Math. Hungar. | 
| 14 \(\Rightarrow\) 52 | On the application of Tychonoff's theorem in mathematical proofs, L o's,  J. 1951, Fund. Math. Two applications of the method of construction by ultrapowers to analysis, Luxemburg, W.A.J. 1970, Proc. Symp. Pure. Math. Applications of Model Theory to Algebra, Analysis and Probability, Luxemburg, 1969, 123-137 | 
| 52 \(\Rightarrow\) 309 | The Hahn-Banach theorem implies the Banach-Tarski paradox, Pawlikowski,  J. 1991, Fund. Math. | 
Here are the links and statements of the form equivalence classes referenced above:
| Howard-Rubin Number | Statement | 
|---|---|
| 50: | Sikorski's Extension Theorem: Every homomorphism of a subalgebra \(B\) of a Boolean algebra \(A\) into a complete Boolean algebra \(B'\) can be extended to a homomorphism of \(A\) into \(B'\). Sikorski [1964], p. 141. | 
| 14: | BPI: Every Boolean algebra has a prime ideal. | 
| 52: | Hahn-Banach Theorem: If \(V\) is a real vector space and \(p: V \rightarrow {\Bbb R}\) satisfies \(p(x+y) \le p(x) + p(y)\) and \((\forall t > 0)( p(tx) = tp(x) )\) and \(S\) is a subspace of \(V\) and \(f:S \rightarrow {\Bbb R}\) is linear and satisfies \((\forall x \in S)( f(x) \le p(x) )\) then \(f\) can be extended to \(f^{*} : V \rightarrow {\Bbb R}\) such that \(f^{*}\) is linear and \((\forall x \in V)(f^{*}(x) \le p(x))\). | 
| 309: | The Banach-Tarski Paradox: There are three finite partitions \(\{P_1,\ldots\), \(P_n\}\), \(\{Q_1,\ldots,Q_r\}\) and \(\{S_1,\ldots,S_n, T_1,\ldots,T_r\}\) of \(B^3 = \{x\in {\Bbb R}^3 : |x| \le 1\}\) such that \(P_i\) is congruent to \(S_i\) for \(1\le i\le n\) and \(Q_i\) is congruent to \(T_i\) for \(1\le i\le r\). | 
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