[xsl] Using "except" where some nodes are copies (not the original)?

["Costello, Roger L." <costello@xxxxxxxxx>]

Hi Folks,

How do I do set subtraction where some of the nodes in the two sets may be
copies (not originals)?

Please allow me to explain.

Consider this XML document:

<Test>
    <A/>
    <B/>
    <C/>
</Test>

Set <Test> as the context node.

This operation:

    (A, B,, C) except (B, C)

returns:

    (A)

Nice.

Now, make a copy of B and store it into a variable:

      <xsl:variable name="B" as="element(B)">
                <xsl:copy-of select="B" />
       </xsl:variable>

Run the same operation, but using the variable:

    (A, B, C) except ($B, C)

Returns:

    (A, B)

Ouch!

 I don't want that behavior. I want:

    (A, B, C) except ($B, C)

to return:

    (A)

How do I achieve the behavior I desire?

That is, how do I do set subtraction where some of the nodes in the two sets
may be copies?

/Roger