static O ai_makeTester(Web web, S thing, S property) {
  WebNode node = web_findNodeWithForwardRelations(web, "A standard function that tests", "what", thing, "for property", property);
  if (node == null) fail("No tester for " + thing + " / " + property);
  fS sfName = assertNotNull(web_operandText(node, "is"));
  print("Using function: " + sfName + " for " + thing + " / " + property);
  final Class c = loadFunctions_cached(sfName);
  ret func(O o) { call(c, sfName, o) };
}