private bool Hidden(ChapterInfo pgc)
{
if (checkBoxLessThan20mins.Checked && pgc.Duration < TWENTY) return true;
if (checkBoxLessThan5.Checked && pgc.Chapters.Count < 5) return true;
if (checkBoxGreaterThan50.Checked && pgc.Chapters.Count > 50) return true;
return false;
}