We have the following indirect implication of form equivalence classes:
			
| Implication | Reference | 
|---|---|
| 257 \(\Rightarrow\) 260 | 
							 	Variations of Zorn's lemma, principles of cofinality, and Hausdorff's maximal principle, Part I and II, Harper,  J. 1976, Notre Dame J. Formal Logic  | 
					
| 260 \(\Rightarrow\) 40 | 
							 	Variations of Zorn's lemma, principles of cofinality, and Hausdorff's maximal principle, Part I and II, Harper,  J. 1976, Notre Dame J. Formal Logic  | 
					
| 40 \(\Rightarrow\) 43 | 
							 	Consistency results for $ZF$, Jensen,  R.B. 1967, Notices Amer. Math. Soc.  On cardinals and their successors, Jech, T. 1966a, Bull. Acad. Polon. Sci. S'er. Sci. Math. Astronom. Phys.  | 
					
| 43 \(\Rightarrow\) 279 | 
							 	All operators on a Hilbert space are bounded, Wright,  J.D.M. 1973, Bull. Amer. Math. Soc.  | 
					
Here are the links and statements of the form equivalence classes referenced above:
| Howard-Rubin Number | Statement | 
|---|---|
| 257: | \(Z(TR,P)\): Every transitive relation \((X,R)\) in which every partially ordered subset has an upper bound, has a maximal element.  | 
					
| 260: | \(Z(TR\&C,P)\): If \((X,R)\) is a transitive and connected relation in which every partially ordered subset has an upper bound, then \((X,R)\) has a maximal element.  | 
					
| 40: | \(C(WO,\infty)\): Every well orderable set of non-empty sets has a choice function. Moore, G. [1982], p 325.  | 
					
| 43: | \(DC(\omega)\) (DC), Principle of Dependent Choices: If \(S\) is a relation on a non-empty set \(A\) and \((\forall x\in A) (\exists y\in A)(x S y)\) then there is a sequence \(a(0), a(1), a(2), \ldots\) of elements of \(A\) such that \((\forall n\in\omega)(a(n)\mathrel S a(n+1))\). See Tarski [1948], p 96, Levy [1964], p. 136.  | 
					
| 279: | The Closed Graph Theorem for operations between Fréchet Spaces: Suppose \(X\) and \(Y\) are Fréchet spaces, \(T:X\to Y\) is linear and \(G=\{(x,Tx): x \in X \}\) is closed in \(X\times Y\). Then \(T\) is continuous. Rudin [1991] p. 51.  | 
					
Comment: