Formulas are nice, but let's find out what's really going on: $\theta(0,b)=b\,$ and $\theta(1,b)=1-b$. Much clearer. 

Could $x=1-y\,$ where $x$ and $y$ are natural numbers? Depends on what one means by natural number. It can certainly happen if we allow $0$ to be a natural number.  I am inclined to allow that, out of loyalty to logic, where it is a standard convention.  But I am in a minority. Certainly it cannot happen if $x$ and $y$ are positive.  

Finally, for surjectivity (love that word) is every integer of the form $x$ or $1-y$ where $x$ and $y$ are positive integers? Sure.

Is this function bijective?
In SharePoint Server 2010, say I set up a Document Set and put some Word documents in it. Each Word document contains a common phrase that is found only in the body of the Word Documents.

When searching for this common phrase that exists in each of the Word Documents, is there a way to return only the Document Set in the search results, instead of returning each individual Word document?
