比较两个名单

var commonNames = firstList
                    .Select(m => m.Split('(')[0].Trim())
                    .Intersect(secondList);

与Austin Salonen指出的TextBoxes一样

var firstList = textBox1.Text.Select(m => m.Split(Environment.NewLine));

var secondList = textBox2.Text.Select(m => m.Split(Environment.NewLine));

resultTextBox.Text = string.Join(Environment.NewLine,
                           firstList
                             .Select(m => m.Split('(')[0].Trim())
                             .Intersect(secondList));