static L<WebNode> web_operands(WebNode node) {
  ret web_allForwardRelated(node, "");
}

static L<WebNode> web_operands(WebNode node, S rel) {
  ret web_allForwardRelated(node, rel);
}

static L<WebNode> web_operands(Collection<WebNode> nodes) {
  ret concatMap(f web_operands, nodes);
}