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 \(\Rightarrow\) 49 | A survey of recent results in set theory, Mathias,  A.R.D. 1979, Period. Math. Hungar. | 
| 49 \(\Rightarrow\) 30 | clear | 
| 30 \(\Rightarrow\) 62 | clear | 
| 62 \(\Rightarrow\) 61 | clear | 
| 61 \(\Rightarrow\) 46-K | clear | 
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. | 
| 49: | Order Extension Principle: Every partial ordering can be extended to a linear ordering. Tarski [1924], p 78. | 
| 30: | Ordering Principle: Every set can be linearly ordered. | 
| 62: | \(C(\infty,< \aleph_{0})\): Every set of non-empty finite sets has a choice function. | 
| 61: | \((\forall n\in\omega, n\ge 2\))\((C(\infty,n))\): For each \(n\in\omega\), \(n\ge 2\), every set of \(n\) element sets has a choice function. | 
| 46-K: | If \(K\) is a finite subset of \(\omega-\{0,1\}\), \(C(\infty,K)\): For every \(n\in K\), every set of \(n\)-element sets has a choice function. | 
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