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The melakha of Sewing is defined as attaching things together, such as curtains, pieces of cloth, or pieces of paper. However, extremely temporary connections are permitted. For this reason, diapers may be used, as may sticky notes (because they are designed to be used multiple times).
Attaching things together by tying a knot is the melakha of Tying; separating them by undoing the knot is the melakha of Untying. The forbidden knots are those of a professional (even if they are temporary) or those meant to last for longer than a week. However, a provisional bow or single knot, such as that of a shoe or a kerchief, or that made by a non-professional, may be tied and untied.
The melakha of Tearing is defined as tearing or cutting something for a constructive purpose. For example, it is prohibited to cut cloth to sew it, or to tear off garbage bags or tablecloths from a plastic roll in order to use them. However, it is permissible to tear open a package of food or tissues because the purpose is not to use the packaging but what is inside.
Tearing toilet paper is prohibited on the Torah level. If it is done with a shinui, it is prohibited rabbinically. If one finds himself in a situation where one cannot wipe oneself without tearing toilet paper, one may do so in order to preserve dignity, but must use a shinui (such as doing the tearing with one's elbows or fists).
