We have the following indirect implication of form equivalence classes:
			
| Implication | Reference | 
|---|---|
| 49 \(\Rightarrow\) 30 | clear | 
| 30 \(\Rightarrow\) 377 | clear | 
Here are the links and statements of the form equivalence classes referenced above:
| Howard-Rubin Number | Statement | 
|---|---|
| 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. | 
| 377: | Restricted Ordering Principle: For every infinite set \(X\) there is an infinite subset \(Y\) of \(X\) such that \(Y\) can be linearly ordered. | 
Comment: