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- The Gemara 75b tells us that if someone erases one letter and there’s room for two letters to be drawn in its place he is chayav
- The Pri Megadim raises the suggestion that even though we know that the shiur in order to be chayav for mecheika is two letters still if one were to erase one letter from a sefer that was written in error in order to fix it you would be chayav for mechika because that erasure is instrumental in order to complete the sefer correctly. The Minchas Chinuch suggests that, according to the Rambam, that you are chayav when it is on condition to be constructive one who removes a tattoo on Shabbos would be chayav because it is a tikun.
- The Rambam Shabbos 11:17 writes that a toldah of mocheik would be if one erases a marking, roshem, in order to fix it. The Rosh Shabbos 7:9 however quotes a tosefta and explains it as saying that the fundamental principle to transgress mocheik is the “machshava for ksiva,” for the intent to write, and therefore one would be chayav even for erasing a blur splotch on a page.
Letters on a Cake
- Many poskim permit eating cake that has writing on it but forbid breaking the letters when cutting the cake, while others permit breaking the letters as well.  Sephardim may be lenient. 
- Even for those who are strict it is permitted to cut between letters even if that destroys the word,  if the letters are baked into the cake itself , or if the cake was cut before Shabbat and one simply wants to separate the pieces. 
Letters on a Package
- The Ashkenazic custom is to avoid ripping letters when opening a package on Shabbat, while the Sephardic custom is to be lenient in this issue. 
Removing Wax on Top of Letters
- If ink or wax fell on writing one should not erase the ink or wax because that would be erasing in order to write. 
- If an ink or wax blotch is covering letters of a Sefer Torah and this is found during Torah reading, if one can read the letter through the wax the Torah is fit to be read, but if it’s not readable some say to take out another Torah and some say just to read that word by heart. 
- It is considered a Biblical prohibition to erase in order to write and one example of is where one erases one letter to form another letter or erasing one letter to form two letters such as separating an m into two n’s. 
Writing on the Side of Books
- Many poskim hold that it is permitted to open a book on Shabbat even though it has letters or pictures on the side of the pages of the book; if, however, there is another similar book available without letters on the side, one should use that one. Also, it’s preferable not to write on the sides of books in order to avoid this issue. 
- Mishna Shabbat 7:2, Daf 73a. Rashi 73a writes that erasing is a melacha because the numbers written on the boards were sometimes erased when a board was improperly marked see also Rosh (7:9)
- As opposed to if you only write only letter big enough that two letters could fill its place you are patur, the gemara says this is where we see a chumra by mechika that doesn’t exist by koseiv.
- Mishbesos Zahav 340:1 based on a Yerushalmi and a Rambam.
- Moseich HaShabbos: Mocheik, Os 4
- The Mordechai (Shabbat 369) cites the Maharam as ruling that on Yom Tov, it is rabbinically forbidden to eat cake that has letters written on it. He explains that it only is a rabbinic prohibition because one is erasing without intending to write in the place where he just erased. This is codified in the context of Shabbat by the Rama (O.C. 340:3).
- The Dagul Meirvavah 340 argues that eating the cake should be permitted, since it is only a psik reisha of a rabbinic prohibition that anyway is being done in an abnormal way. He asserts that breaking letters on a cake is an abnormal way of erasing, and certainly breaking the letters in one’s mouth is unusual. Rav Ovadia Yosef (Yabia Omer O.C. 4:38) adds that it should be permitted because it is only a psik riesha d’lo nicha lei on a rabbinic prohibition. Rav Mordechai Willig (“Hilchos Shabbos - Kotev/Mocheik #2,” min 39-43), however, argues that there is room to distinguish between a gezeirah, where psik riesha d’lo nicha lei may apply, and an action that is only d’rabanan because of a general principle, such as doing something in a destructive manner, where such a leniency doesn’t apply.
- The Taz 340:2 also permits because the letters are being broken for the purpose of eating, a leniency found regarding to Borer and Tochen. The Chazon Ish (O.C. 61), however, answers that since chewing and eating always involve Borer and Tochen it is permitted even immediately prior to eating. No such permission was given in the context of erasing.
- Kitzur S”A 80:63 and Aruch HaShulchan 340:23 are lenient, while the Mishna Brurah 340:17, Chazon Ish 61:1, and Shemirat Shabbat Kehilchata 11:7 permit only breaking the letters in one’s mouth, not cutting them with one’s hands prior to eating. Rabbi Zvi Sobolofsky (“Hilchos Shabbos Series Mocheik Removing Letters from a cake” min 15-6) states that the minhag to be strict for the Rama is only a chumra.
- See further: Sh”t Tzitz Eliezer 11:20, Sh”t Beir Moshe 6:92, Sh”t Az Nidabru 10:8, Sh”t Vayeshev Moshe 1:4
- Sh"t Or Litzion 2:40, Sh”t Yabia Omer O”C 4:38, Rabbi Eli Mansour
- Rav Shlomo Zalman Auerbach in Shemirat Shabbat Kihilchita 9: footnote 38
- Mishna Brurah 340:15, Sh"t Har Tzvi 214, Sh"t Or Litzion 2:40
- Rav Shlomo Zalman Auerbach in Shemirat Shabbat Kihilchita 11: footnote 30
- Shemirat Shabbat Kehilchata 9:13 (quoting Rav Shlomo Zalman Auerbach) rules it is only rabbinically forbidden to rip through letters when opening a package, as is not considered erasing in order to write.
- Rabbi Zvi Sobolofsky (“Hilchos Shabbos Series Mocheik Removing Letters from a cake” min 18) explains that strictly speaking, it should be permitted to tear through letters for the same reasons that the Dagul Meirvavah permitted cutting letters on a cake. The minhag, though, is to be strict. Yalkut Yosef (Shabbat vol 5, p. 117) permits tearing through letters because it is a psik reisha d’lo nicha lei on a rabbinic prohibition.
- Mishna Brurah 340:10
- Yabia Omer vol. 4 Orach Chaim 15:3, Mishna Brurah 340:10
- Mishna Brurah 340:22(4)
- Birkei Yosef 340:5, Leviat Chen 120, Sh"t Tzitz Eliezer 13:44, Vayesh Moshe 1:65, Mishna Berura 340:17.
- The Levush 340:4 writes that it is a Torah violation to open or close a book with words stamped on the sides of the pages. He maintains that opening the book is erasing because the letters are broken, and then closing the book again is writing because the letters are reformed. Magen Avraham 340:6 and Chazon Ish 61:1 are machmir for this Levush.
- The Rama in a teshuva (119), however, is lenient based on the Gemara Shabbat (104b) that says that there is a biblical prohibition if a person writes one letter in Tiveriya and one in Tzipori because it is not considered lacking a significant action to bring them together. The Rama infers that moving letters closer to or further from one another is not considered writing or erasing. Similarly, opening the book doesn’t erase the letters, but merely separates the parts of the letters, and closing the book doesn’t write the letters, but just combines the halves.
- The Avnei Neizer 210:1-3 rejects this proof. He argues that separating two letters isn’t considered erasing because the letters still exist, but splitting letters horizontally is considered erasing because the letters become nonexistent. See Rama (ibid.) and Taz 340:2 for resolutions to this difficulty.
- However, Sh"t Rama 119 and Taz 340:2 disagree saying that bringing existing letters together isn't a melacha and since the book is meant to be open and closed it is like opening and closing a door which is certainly permissible and not an issue of boneh and soter. The Rama's leniency is based on the Gemara Shabbat (104b) that says that there is a biblical prohibition if a person writes one letter in Tiveriya and one in Tzipori because it is not considered lacking a significant action to bring them together. The Rama infers that moving letters closer to or further from one another is not considered writing or erasing. Similarly, opening the book doesn’t erase the letters, but merely separates the parts of the letters, and closing the book doesn’t write the letters, but just combines the halves. The Avnei Neizer 210:1-3 rejects this proof. He argues that separating two letters isn’t considered erasing because the letters still exist, but splitting letters horizontally is considered erasing because the letters become nonexistent. See Rama (ibid.) and Taz 340:2 for resolutions to this difficulty. Based on this Avnei Nezer, see also Sh"t Har Tzvi Melechet Kotev 4 writes that even the Levush himself agrees that separating two complete letters isn't an issue of writing. He is just concerned of joining and separating letter fragments but not separating two whole letters.
- Halacha for Ashkenazim: Mishna Brurah 340:17 comments that the minhag is to follow the Rama, yet if one has another sefer without letters on the side, he should use that one instead to be strict for the Levush. Shemirat Shabbat KeHilchata 28:2 writes that it is preferable not to open a book with words or pictures written across the edge of their leaves and are broken and put back together when the book is opened and closed. He concludes that many authorities permit opening the book in such a case. The problem is best avoided by not writing on the edge of books.
- Halacha for Sephardim: Yalkut Yosef (340:8 Din Kotev BeShabbat) writes that it is permitted according to the strict law, however, initially one should avoid writing words on the side of Sefarim.