static S ai_subst_web(S webID) {
  int n = websMadeInThread();
  Web web = assertNotNull("Web not found: " + webID, ai_getWeb(webID));
  WebRelation rel = assertNotNull(web_findRelationNamed(web, "matches"));
  S pat = web_unquoted(rel.a), input = web_unquoted(rel.b);
  assertEquals("substitute * => * with *", pat);
  new Matches m;
  assertTrue(flexMatchIC(pat, input, m));
  S src = unquote(m.get(0));
  L<S> terms = unquoteAll(trimAll(splitAtJavaToken(m.get(1), ",")));
  ai_postTriple_multi(src, "see:", terms);
  ret nWebs(websMadeInThread()-n) + " made";
}