static Web webFromTriples(Symbol... l) {
  Web web = simpleWeb();
  for (int i = 0; i < l(l); i += 3) {
    S a = unnull(asString(get(l, i))), b = unnull(asString(get(l, i+1))), c = unnull(asString(get(l, i+2)));
    web_addRelation(web, a, c, b);
  }
  ret web;
}

static Web webFromTriples(L<Symbol> l) {
  ret webFromTriples(toSymbolArray(l));
}