assert !symbol.isNone() && !symbol.isError();
            public LinkedList getOwners(Symbol symbol) {                LinkedList owners = new LinkedList();                while (true) {                    owners.addFirst(symbol);                    if (symbol.isRoot()) break;                    if (symbol.isNone()) break;                    if (symbol.isError()) break;                    symbol = symbol.owner();                }                return owners;            }