Use "with" rather than "when" to name a context that defines a Given

Hi.  Looks like your sample code generally uses "with" to describe contexts that contain Givens, and "when" to describe contexts that contain "when".  But there was one case of a Given context that was described with "when".  

To minimize (my own) confusion regarding Givens vs Whens I figured I'd change it to use a "with" for that context as well.