2012/1/10 David Carlisle <davidc@xxxxxxxxx>:
>
> $elements[not(some $e in $elementSubset satisfies . is $e)]
>

2012/1/10 Michael Kay <mike@xxxxxxxxxxxx>:
>
> $X[not(. intersect $Y)]
>

Thanks Michael and David for two equally useful solutions.  Helpful
and competent as always.

Thomas W.