Understanding the type of knots that are allowed to be opened on Shabbos.
דבר דבר (Dabair Davar): Addition 1 to 1542: Going to ארץ ישראל Eretz Yisroel; Saying תהילים Tehillim for a Sick Person;
pulling out a plug from the wall; removing ice attached to the window, door; removing paint cement from door or window;