code: public static boolean has(Xml root, String formula)
      {
          Check.notNull(root);
          Check.notNull(formula);
  
          for (final Xml node : root.getChildren(NODE_FORMULA))
          {
              if (node.readString(ATT_NAME).equals(formula))
              {
                  return true;
              }
          }
          return false;
      }
docs: Check if node has formula node.
  
  @param root The root node (must not be <code>null</code>).
  @param formula The formula name to check (must not be <code>null</code>).
  @return <code>true</code> if has formula, <code>false</code> else.
  @throws LionEngineException If invalid argument.