We have the following indirect implication of form equivalence classes:
			
| Implication | Reference | 
|---|---|
| 239 \(\Rightarrow\) 427 | clear | 
| 427 \(\Rightarrow\) 67 | clear | 
| 67 \(\Rightarrow\) 89 | On cardinals and their successors, Jech,  T. 1966a, Bull. Acad. Polon. Sci. S'er. Sci. Math. Astronom. Phys. | 
| 89 \(\Rightarrow\) 90 | The Axiom of Choice, Jech, 1973b, page 133 | 
| 90 \(\Rightarrow\) 91 | The Axiom of Choice, Jech, 1973b, page 133 | 
| 91 \(\Rightarrow\) 79 | clear | 
| 79 \(\Rightarrow\) 70 | clear | 
Here are the links and statements of the form equivalence classes referenced above:
| Howard-Rubin Number | Statement | 
|---|---|
| 239: | AL20(\(\mathbb Q\)): Every vector \(V\) space over \(\mathbb Q\) has the property that every linearly independent subset of \(V\) can be extended to a basis. Rubin, H./Rubin, J. [1985], p.119, AL20. | 
| 427: | \(\exists F\) AL20(\(F\)): There is a field \(F\) such that every vector space \(V\) over \(F\) has the property that every independent subset of \(V\) can be extended to a basis. \ac{Bleicher} \cite{1964}, \ac{Rubin, H.\/Rubin, J \cite{1985, p.119, AL20}. | 
| 67: | \(MC(\infty,\infty)\) \((MC)\), The Axiom of Multiple Choice: For every set \(M\) of non-empty sets there is a function \(f\) such that \((\forall x\in M)(\emptyset\neq f(x)\subseteq x\) and \(f(x)\) is finite). | 
| 89: | Antichain Principle: Every partially ordered set has a maximal antichain. Jech [1973b], p 133. | 
| 90: | \(LW\): Every linearly ordered set can be well ordered. Jech [1973b], p 133. | 
| 91: | \(PW\): The power set of a well ordered set can be well ordered. | 
| 79: | \({\Bbb R}\) can be well ordered. Hilbert [1900], p 263. | 
| 70: | There is a non-trivial ultrafilter on \(\omega\). Jech [1973b], prob 5.24. | 
Comment: