mainPanel.add(expressionCheck, "wrap, center");
mainPanel.add(insertOperatorButton, "span 2, right, split 2");
mainPanel.add(insertVariableButton, "right, wrap");
mainPanel.add(expressionCheck, "wrap, center");
mainPanel.add(insertOperatorButton, "span 2, right, split 2");
mainPanel.add(insertVariableButton, "right, wrap");