static Web web_ifThen(Web inputWeb, Web web) {
  Web patternWeb, Map<WebNode> patternMap = unpair cloneWebWithMap(web);
  web_dropRelationsStartingWith(patternWeb, "Then:");

  Web thenWeb, Map<WebNode> thenMap = unpair cloneWebWithReverseMap(web);
  web_unpackRelationsStartingWith(thenWeb, "Then:");
  
  Map<WebNode> match = web_matchAllPerms_partial(patternWeb, inputWeb);
  
  if (match != null) {
    // Then add relations from thenWeb
    for (WebRelation rel : web_relationObjects(thenWeb)) {
      WebNode a = mapGet(match, mapGet(patternMap, mapGet(thenMap, rel.a));
      WebNode b = mapGet(match, mapGet(patternMap, mapGet(thenMap, rel.b));
      if (a != null && b != null) {
        WebRelation rel2 = inputWeb.getRelation(a, b);
        web_addLabelsFromNodeToNode(rel, rel2);
      }
    }
  }
  
  ret inputWeb;
}