We have the following indirect implication of form equivalence classes:
			
| Implication | Reference | 
|---|---|
| 302 \(\Rightarrow\) 301 | Some propositions equivalent to the Sikorski extension theorem for Boolean algebras, Bell,  J.L. 1988, Fund. Math. | 
| 301 \(\Rightarrow\) 300 | Some propositions equivalent to the Sikorski extension theorem for Boolean algebras, Bell,  J.L. 1988, Fund. Math. | 
Here are the links and statements of the form equivalence classes referenced above:
| Howard-Rubin Number | Statement | 
|---|---|
| 302: | Any continuous surjection between compact Hausdorff spaces has an irreducible restriction to a closed subset of its domain. | 
| 301: | Any continuous surjection between Boolean spaces has an irreducible restriction to a closed subset of its domain. | 
| 300: | Any continuous surjection between extremally disconnected compact Hausdorff spaces has an irreducible restriction to a closed subset of its domain. | 
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