:To find the quote you request, you need only follow the link from "statement" to get the definition in Hamilton, "A statement is a declarative sentence that is either true or false." 

 :Keep in mind that I'm not talking philosophy here, only mathematics. 

 :In mathematics  in Hamilton in particular  we have (parapharse, because it is Sunday and my Hamilton is out at school): 

 :::Proposition 3.5:  If a group is cyclic then it is abelian. 

 :::Proof:  

 :Clearly, in this usage, which is common, "proposition" means "true proposition". 

 :I'll rewrite to make this clear to the reader.  If you agree it is now clear, you can remove the "fact" tags.