[xsl] Need an XPath expression for: $B is not contained in $A

["Costello, Roger L. costello@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Hi Folks,

The variable $A contains an element.

The variable $B contains an element.

I need an XPath expression that determines if $B is not contained in $A.

This XPath expression seems to work:

    not(index-of($B/ancestor::*,$A))

but that seems awful, i.e., not straightforward, convoluted, and probably
inefficient.

Is there a better (simpler, straightforward, efficient) XPath expression?

/Roger