Item ArgumentReference::evaluateSingleton(const DynamicContext::Ptr &context) const
{
    return context->expressionVariable(slot())->evaluateSingleton(context);
}
Item::Iterator::Ptr ArgumentReference::evaluateSequence(const DynamicContext::Ptr &context) const
{
    return context->expressionVariable(slot())->evaluateSequence(context);
}
bool ExpressionVariableReference::evaluateEBV(const DynamicContext::Ptr &context) const
{
    return context->expressionVariable(slot())->evaluateEBV(context);
}