We have the following indirect implication of form equivalence classes:
			
| Implication | Reference | 
|---|---|
| 14 \(\Rightarrow\) 49 | A survey of recent results in set theory, Mathias,  A.R.D. 1979, Period. Math. Hungar. | 
| 49 \(\Rightarrow\) 30 | clear | 
| 30 \(\Rightarrow\) 198 | clear | 
Here are the links and statements of the form equivalence classes referenced above:
| Howard-Rubin Number | Statement | 
|---|---|
| 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. | 
| 198: | For every set \(S\), if the only linearly orderable subsets of \(S\) are the finite subsets of \(S\), then either \(S\) is finite or \(S\) has an amorphous subset. | 
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