Re: [xsl] Need your recommendation please for an XPath expression

["David Carlisle d.p.carlisle@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

On 19 July 2016 at 13:05, Costello, Roger L. costello@xxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
> Hi Folks,
>
> I need an XPath expression which returns a Boolean value:
>
>         If there is an A then return true only if there is a B.
>         If there is no A then return true.
>
> For example, the XPath expression should return true for this:
>
> <Document>
>     <A/>
>     <B/>
> </Document>
>
> The XPath should return false for this:
>
> <Document>
>     <A/>
> </Document>
>
> Which XPath expression is best (most efficient)?
>
> (a)   if (A) then exists(B) else true()
>
> (b)  (A and B) or (not(A))
>
> (c)  something else (what?)
>

not(A) or B