private Item intern(Item item) { if (item.sameSymbol(ANY.getSymbol())) return ANY; if (item.sameSymbol(VAR.getSymbol())) return VAR; if (item.sameSymbol(TERM.getSymbol())) return TERM; if (item.sameSymbol(URI.getSymbol())) return URI; if (item.sameSymbol(LITERAL.getSymbol())) return LITERAL; if (item.sameSymbol(BNODE.getSymbol())) return BNODE; return item; }