Understanding the type of knots that are allowed to be opened on Shabbos.
Interesting question in reference to texting, emails or phone call.
A few very important points in reference to 'הכנה משבת לחול' (doing an action on Shabbos for a weekday);
Folding Garments on Shabbos, קיפול בגדים (Kipul Begadim). How הכנה (Hachana) Has to Do With Folding Garments on Shabbos;