private void btnVariableActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_btnVariableActionPerformed
        f.setBounds(this.getX() + this.getWidth(), this.getY(), 150, this.getHeight());
        MathList<Variable> variable = f.VariableList();
        vari = true;
        f.repaint();
        f.setVisible(true);
    }//GEN-LAST:event_btnVariableActionPerformed