private Boolean addBracketOpen(CalculatorReader expressionReader) {
        String el = expressionReader.getSymbol();
        if (el.equals("(")) {
            //System.out.println("--addBracketOpen = " + el);
            expressionReader.incPosition();
            expressionStack.bracketStack.push(expressionStack.operatorStack.size());
            return true;
        }
        return false;
    }