First Discussion: Are there avos and toldos in the rest of the Torah?

וְתִיפּוֹק לֵיהּ לְחִלּוּק מְלָאכוֹת מֵהֵיכָא דְּנָפְקָא לֵיהּ לְרַבִּי יוֹסֵי! דְּתַנְיָא, רַבִּי יוֹסֵי אוֹמֵר: ״וְעָשָׂה מֵאַחַת מֵהֵנָּה״, פְּעָמִים שֶׁחַיָּיבִים אַחַת עַל כּוּלָּן, וּפְעָמִים שֶׁחַיָּיבִין עַל כׇּל אַחַת וְאַחַת. וְאָמַר רַבִּי יוֹסֵי בְּרַבִּי חֲנִינָא: מַאי טַעְמָא דְּרַבִּי יוֹסֵי, ״אַחַת״ ״מֵאַחַת״, ״הֵנָּה״ ״מֵהֵנָּה״ — אַחַת שֶׁהִיא הֵנָּה, הֵנָּה שֶׁהִיא אַחַת. ״אַחַת״ — שִׁמְעוֹן. ״מֵאַחַת״ —שֵׁם מִשִּׁמְעוֹן. ״הֵנָּה״ — אָבוֹת, ״מֵהֵנָּה״ — תּוֹלָדוֹת.

The Gemara raises an additional challenge to Shmuel’s opinion. If he holds in accordance with the opinion of Rabbi Yosei with regard to the explicit prohibition of kindling, let him derive the division of labors from where Rabbi Yosei derives it. As it was taught in a baraita that Rabbi Yosei says, it is stated: “Speak to the children of Israel, saying: A soul that sins in error, from all the commandments of God that may not be performed, and performs from one of them [me’aḥat me’hena]” (Leviticus 4:2). Rabbi Yosei interprets the verse that at times one is liable to bring one sin-offering for all of his transgressions, and at times one is liable to bring a sin-offering for each and every transgression. And Rabbi Yosei, son of Rabbi Ḥanina, said: What is the rationale for the opinion of Rabbi Yosei? He interprets the unique phrase employed in that verse: From one of these. The Torah could have merely stated: One [aḥat]. Instead, it stated: From one [me’aḥat]. It could have merely stated: Them [hena]. Instead, it stated: Of them [me’hena]. Rabbi Yosei derives that there are cases of one transgression that, with regard to punishment, are them, i.e., many. And there are cases of them, several transgressions, that, with regard to punishment, are one.

גמ׳ מדקתני אבות מכלל דאיכא תולדות.

MISHNA: There are four primary categories of damage: The category of Ox; and the category of Pit; and the category of Maveh, which, based on a discussion in the Gemara refers either to the tooth of an animal that causes damage or to a person who causes damage; and the category of Fire. Each of these categories is unique; therefore, the halakhot of one cannot be derived from another. The defining characteristic of the primary category of Ox is not similar to the defining characteristic of the primary category of Maveh, and the defining characteristic of the primary category of Maveh is not similar to the defining characteristic of the primary category of Ox. And the defining characteristics of this category of Ox and that category of Maveh, in which there is a living spirit that causes damage, are not similar to the defining characteristic of the category of Fire, in which there is no living spirit. The mishna continues: And the defining characteristics of this primary category of Ox and Maveh and that primary category of Fire, in which the typical manner of their components is to proceed from one place to another and cause damage, are not similar to the defining characteristic of the primary category of Pit, in which the typical manner of its components is not to proceed from one place to another and cause damage; rather, it remains in place and the damage is caused by the injured party proceeding and encountering the obstacle. The common denominator of the components in all of these primary categories is that it is their typical manner to cause damage, and the responsibility for their safeguarding to prevent them from causing damage is incumbent upon you, the owner of the animal or generator of the fire or the pit. And when a component of any of these categories causes damage, the owner or generator of the component that caused the damage is obligated to pay restitution for damage with best-quality land. GEMARA: From the fact that the mishna teaches its ruling employing the term: Primary categories, by inference, there are subcategories of those primary categories. The Gemara asks: Are their subcategories similar to them, i.e., to their respective primary categories, so that the same halakhot apply to them, or are they dissimilar to them? The Gemara cites additional areas of halakha where there are primary categories and subcategories and considers the relationship between them: With regard to Shabbat we learned in a mishna (Shabbat 73a): The primary categories of labor prohibited on Shabbat number forty-less-one. There too, from the fact that the mishna teaches its ruling employing the term: Primary categories, by inference, there are also subcategories. With regard to the primary categories of labor prohibited on Shabbat, their subcategories are similar to them, as it is no different if one unwittingly performed labor that is a primary category, for which he is liable to bring a sin-offering, and it is no different if one unwittingly performed labor that is a subcategory, for which he is liable to bring a sin-offering. Likewise, it is no different if one intentionally performed labor that is a primary category, for which he is liable to be executed by stoning, and it is no different if one intentionally performed labor that is a subcategory, for which he is liable to be executed by stoning. And what difference is there between a primary category and a subcategory? The Gemara explains: The practical difference is that if one unwittingly performs two labors classified as different primary categories together, during a single lapse of awareness, or, alternatively, if one unwittingly performs two labors classified as subcategories of two different primary categories together, during a single lapse of awareness, one is liable to bring a sin-offering for each and every labor that he performed. Each primary category of labor is an independent transgression. While if one unwittingly performs a labor that is a primary category and another labor classified as its subcategory during a single lapse of awareness, he is liable to bring only one sin-offering. The Gemara asks: And according to Rabbi Eliezer, who deems one liable to bring two sin-offerings even if one performs a labor classified as a subcategory together with a labor that is its primary category, why is one labor characterized as a primary category and why is the other labor characterized as a subcategory? The Gemara explains: Of the labors prohibited on Shabbat, that which was a significant labor in the Tabernacle, the Sages characterized it as a primary category, and that which was not a significant labor in the Tabernacle, the Sages characterized it as a subcategory. The labors prohibited on Shabbat are derived from the labors employed in the construction of the Tabernacle; therefore, their classification is also based on their significance in its construction. With regard to ritual impurities, we learned in the mishna (Kelim 1:1): The primary categories of ritual impurity are as follows: Any of the eight species of the creeping animal enumerated in the Torah (Leviticus 11:29–30), and semen,

תימה: לר' מאי שנא דתולדה דשבת ילפינן לה מקראי בפרק הבונה דרשינן הנה אבות מהנה תולדות ותולדות דנזקין לא ילפינן מקראי אלא מסברא לקמן בשמעתין. ונראה למהר"י כ"ץ אי לאו קרא הוה ממעטינן תולדות מדנסמכה פרשת שבת למלאכת המשכן כי היכי דממעטינן שאר מלאכות דלא הוו חשיבי.

מתני׳ רבי יוסי בן המשולם אומר השוחט את הבכור עושה מקום בקופיץ מיכן ומיכן ותולש את השער ובלבד שלא יזיזנו ממקומו וכן תולש את השער לראות מקום מום:
MISHNA: Rabbi Yosei ben HaMeshullam says: Since it is prohibited by Torah law to shear a firstborn, as it states: “And you shall not shear the firstborn of your flock” (Deuteronomy 15:19), one who is slaughtering a firstborn, and must clear hair or wool from the area of the neck in order to facilitate proper slaughter, clears space by uprooting the hair with a cleaver [bekofitz] from here and from there, on either side of the neck, although he thereby plucks out the hair. He may clear space in this manner provided that he does not move the plucked hair from its place; it must remain intermingled with the rest of the hair so it will appear that he did not shear the animal. And likewise, one plucks the hair to enable one of the Sages to examine the place of a blemish and thereby determine whether it is permitted to slaughter the firstborn outside the Temple.

ותולש לאו היינו גוזז והתניא התולש את הכנף והקוטמו והמורטו חייב שלש חטאות ואמר ר"ל תולש חייב משום גוזז קוטם חייב משום מחתך ממרט חייב משום ממחק שאני כנף דהיינו אורחיה.

The Gemara raises a difficulty: And can it be claimed that plucking is not considered a form of shearing? But isn’t it taught in a baraita: One who unwittingly plucks a large feather from the wing of a bird on Shabbat, and one who snips the tip of the feather, and one who pulls out the thin threads that constitute the feather is obligated to bring three sin offerings, one for each transgression. And Reish Lakish says, in explanation: One who plucks the wing is liable due to the labor of shearing. One who snips the tip of the feather is liable due to the labor of cutting. And one who pulls out the threads is liable due to the labor of smoothing. The Gemara explains: Plucking a wing is different from plucking hair, as that is the normal method employed to remove feathers.

ואמר ר"ל חייב משום גוזז - תימה מה הוא מקשה אע"ג דלענין בכור לא מחייב ביה משום לא תגוז לענין שבת יש לחייב משום תולדה דגוזז.

Why do we need a source by Shabbos for toldos?

Mahari Katz: The passuk narrowly defines melachos shabbos, so we need the passuk to mechadesh that there are still toldos. In general, however, we assume that something has toldos.

Tosfos: We always assume there are no toldos, shabbos is an exception (and therefore he asks why the Gemara is comparing bechoros to Shabbos).

-Nezikin is self evident that there will be avos and toldos.

Now we will discuss the nafka minos.

(ט) וְכָל הָעוֹבֵד שָׁם עֲבוֹדָה בְּגוּפָהּ שֶׁל קַרְקַע כְּגוֹן שֶׁחָרַשׁ אוֹ חָפַר אוֹ זָרַע אוֹ נָטַע וְכַיּוֹצֵא בָּאֵלּוּ הֲרֵי זֶה לוֹקֶה.

(9) It is forbidden ever to sow seeds or till the river in which the calf was decapitated, as Deuteronomy 21:4 states: "that must never be worked or sown." Whoever performs work with the land itself - e.g., he plowed, he dug, he seeded, he planted, or the like - should be punished with lashes.
It is, however, permitted to comb flax there, or to drill stones, for this is similar to weaving a garment there or sewing it there, for these are tasks that are not performed with the land itself. To emphasize this concept, the verse states: "that must never be worked or sown." Implied is that just as sowing involves the land itself, similarly all work that is forbidden there involves the land itself.

מנחת חינוך, מצוה תקלא

והנה הר"מ כתב חרש או חפר או זרע או נטע וכיוצא באלו כו' אפשר הכוונה כיוצא באלו כמ"ש בפ"ז מהלכות שבת בכלל חרישה הוא חפירה ועושה חריץ, ובכלל זורע הוא נוטע והברכ' והרכבה והזומר וכל אלו הם אבות מלאכות שזומר והברכה כו' הם ענין אחד של זורע וחריץ הוא ענין א' עם חרישה כמו שכ' הר"מ שם ויש עוד תולדות גבי שבת כמבוא' שם בפ"ח מנכש ומקרסם תולדות חורש כו' ומשקה צמחי' תולדת זורע.

-The Rambam, according to the minchas chinuch, holds like mahari katz.

(א) שלא להוציא מבשר הפסח חוצה - לא להוציא מבשר הפסח ממקום החבורה, (פסחים פה, ב) שנאמר (שמות יב מו) לא תוציא מן הבית מן הבשר חוצה.

(ב) משרשי מצוה זו. מה שכתבנו לזכר נסי מצרים. ומפני שנעשנו בני חורין ואדונים באה המצוה עליו שיהא נאכל במקום החבורה ולא נוציאהו לחוץ, כדרך מלכי ארץ, שכל המוכן להם נאכל בהיכלם ברב עם שלהם. ודלת הארץ בעת יכינו סעדה גדולה, ישלחו ממנה לחוץ מנות לרעיהם, לפי שהוא חדוש אצלם.

(1) Not to take out from the meat of the Pesach offering outside: Not to take from the meat of the Pesach offering out of the place of the assemblage (Pesachim 85b), as it is stated (Exodus 12:46), "you shall not take any of the meat outside the house."

(2) From the roots of this commandment is that which we have written - to remember the miracles of Egypt. And since we were made into free men and lords, this commandment came to us that we should eat [it] in the place of the assemblage and not take it outside - like the kings of the land. As everything that is prepared for them is eaten in their chambers with their large retinues. But when the poor of the land prepare a large meal, they send portions to their friends outside, since it is a novelty for them (to have a lavish meal).

(3) The laws of the commandment - for example, what is the law of [the] meat when he takes [it] out (Pesachim 85a); the border that they must make (Mishneh Torah, Laws of Paschal Offering 9:3); the law of a partition between two assemblages that is breached (Pesachim 60b); and the rest of its details - are [all] elucidated in Pesachim.

(4) And [it] is practiced at the time of the [Temple] by males and females. And one who transgresses it and takes of the meat outside violates a negative commandment. And we administer lashes for it - and that is when he dislodges [it] from the house and places [it] outside, like the well-known law about [carrying on] Shabbat (Pesachim 60b).

אָמַר רַבִּי אַמֵּי: הַמּוֹצִיא בְּשַׂר פֶּסַח מֵחֲבוּרָה לַחֲבוּרָה, אֵינוֹ חַיָּיב עַד שֶׁיַּנִּיחַ. הוֹצָאָה כְּתִיב בֵּיהּ כְּשַׁבָּת: מָה שַׁבָּת — עַד דְּעָבֵד עֲקִירָה וְהַנָּחָה, אַף הָכָא נָמֵי — עַד דְּעָבֵד עֲקִירָה וְהַנָּחָה.

Rabbi Ami said: One who carries out the meat of the Paschal lamb from the location of one group to another group is not liable until he places the meat in the location of the second group. The reason for this is that the term carrying out is written about it, as the Torah says: “You shall not carry out,” which is similar to the prohibited labor of the same name pertaining to Shabbat. Therefore, just as when it comes to Shabbat one is not liable for carrying from one domain to another until he performs an act of lifting from one domain and placing in the other domain, so too, here also one is not liable until he performs an act of lifting the meat from the location of one group and placing it in the location of another group.

ומבואר בש"ס ובר"מ והרהמ"ח דאינו חייב על הוצאה זו של פסח עד שיניח דהוצאה כתיב בה כשבת מה שבת וכו' ה"נ עד דעביד עקירה והנחה ע' דף פ"ה ובשבת ד' מבואר דבעינן עקירה והנחה במקום ד' על ד' וע"ש בש"ס כ"פ ובר"מ פי"ג מה"ש אם כן אפשר דכאן נמי בעינן עקירה והנחה במקום דע"ד כיון דאיתקש לשבת... ונ"ל דתלי בשני טעמים שבתוס' שבת ד' ד"ה והא בעינן דר"ת מפרש דאין רגילות להניח מפחות מדע"ד ומסתמא כן הוי במשכן אם כן דוקא בשבת כל דל"ה במשכן אין חייבים אבל כאן חייב דאין ענין למשכן והר"י מפרש שם דאל יצא שם בשבת משמע מקום החפץ ואין מקום חשוב פחות מד' וא"כ כיון דנפקא לי' מאל יוציא אם כן כאן נמי צריך עקירה מעל מקום דע"ד והנחה במקום דע"ד.

Nafka Mina #2:

Minchas Chinuch then discusses whether toldos apply.

However, lichora, it's taluy on the machlokes between M.K. and Tosfos:

-Mahari Katz would say yes.

-Tosfos would say no.

מַשְׁקִין בֵּית הַשְּׁלָחִין בַּמּוֹעֵד וּבַשְּׁבִיעִית.

MISHNA: One may irrigate a field that requires irrigation on the intermediate days of a Festival as well as during the Sabbatical Year, both from a newly emerged spring that began to flow only during the Festival, and from a spring that did not just emerge and that has been flowing for some time. However, one may not irrigate a field with rainwater collected in a cistern, a procedure that requires excessive exertion, or with water drawn with a shadoof [kilon], a lever used to raise water with a bucket from deep down in a well.

אִתְּמַר: הַמְנַכֵּשׁ וְהַמַּשְׁקֶה מַיִם לִזְרָעִים בְּשַׁבָּת, מִשּׁוּם מַאי מַתְרִינַן בֵּיהּ?... תְּנַן: מַשְׁקִין בֵּית הַשְּׁלָחִין בַּמּוֹעֵד וּבִשְׁבִיעִית. בִּשְׁלָמָא מוֹעֵד, מִשּׁוּם טִירְחָא הוּא, וּבִמְקוֹם פְּסֵידָא שָׁרוּ רַבָּנַן. אֶלָּא שְׁבִיעִית, בֵּין לְמַאן דְּאָמַר מִשּׁוּם זוֹרֵעַ וּבֵין לְמַאן דְּאָמַר מִשּׁוּם חוֹרֵשׁ, זְרִיעָה וַחֲרִישָׁה בִּשְׁבִיעִית מִי שְׁרֵי? אָמַר אַבָּיֵי: בִּשְׁבִיעִית בִּזְמַן הַזֶּה, וְרַבִּי הִיא. דְּתַנְיָא, רַבִּי אוֹמֵר: ״וְזֶה דְּבַר הַשְּׁמִטָּה שָׁמוֹט״. בִּשְׁתֵּי שְׁמִיטוֹת הַכָּתוּב מְדַבֵּר, אַחַת שְׁמִיטַּת קַרְקַע, וְאַחַת שְׁמִיטַּת כְּסָפִים. רָבָא אָמַר: אֲפִילּוּ תֵּימָא רַבָּנַן — אָבוֹת אָסַר רַחֲמָנָא, תּוֹלָדוֹת לָא אָסַר רַחֲמָנָא. דִּכְתִיב: ״וּבַשָּׁנָה הַשְּׁבִיעִית שַׁבַּת שַׁבָּתוֹן יִהְיֶה לָאָרֶץ שָׂדְךָ לֹא תִזְרָע וְגוֹ׳״. מִכְּדֵי, זְמִירָה בִּכְלַל זְרִיעָה, וּבְצִירָה בִּכְלַל קְצִירָה. לְמַאי הִלְכְתָא כַּתְבִינְהוּ רַחֲמָנָא? לְמֵימְרָא דְּאַהָנֵי תּוֹלָדוֹת מִיחַיַּיב, אַאַחְרָנְיָיתָא לָא מִיחַיַּיב.

§ It was stated that the amora’im disputed the following question: With regard to one who weeds or one who waters seedlings on Shabbat, for what prohibited labor do we forewarn him? Judicial punishment may be administered to a sinner only if he has been forewarned by two witnesses prior to the commission of his offense. This forewarning must include the specific transgression being violated, and on Shabbat it must include the specific category of prohibited labor that the action involves. Rabba said: It is due to the prohibition against plowing. Rav Yosef said: It is due to the prohibition against sowing. Rabba said: According to my opinion it is reasonable. Just as the usual objective of plowing is to loosen the earth, so too, this, weeding or watering, loosens the earth. Rav Yosef said: According to my opinion, it is reasonable. Just as the usual objective of sowing is to cause the fruit to grow, here too, weeding or watering causes the fruit to grow. Abaye said to Rabba: According to your opinion, it is difficult, and according to the opinion of Rav Yosef, it is difficult. Abaye explains: According to your opinion, it is difficult: Is it true that for the prohibition against plowing, yes, he is forewarned, but for the prohibition against sowing, no, he is not forewarned? Similarly, according to the opinion of Rav Yosef, it is difficult: Can it be that for the prohibition against sowing, yes, he is forewarned, but for the prohibition against plowing, no, he is not forewarned? Everyone should agree that weeding and watering fall under the categories of both plowing and sowing. And if you say that anywhere that there are two possible categories of prohibited labor into which a particular action might fall, one is liable to be punished for only one of them, didn’t Rav Kahana say: If one prunes the branches of a vine on Shabbat and he needs the wood for firewood or any other purpose, he is liable to bring two sin-offerings? He is liable to bring one sin-offering for violating the primary category of sowing, as pruning vines facilitates their growth, and so it is a sub-category of sowing. And he is liable to bring one sin-offering for violating the primary category of reaping, as the essence of reaping is detaching that which one needs from the ground. Since he needs the wood that he is detaching from the vine, his action is considered reaping. Consequently, one action that incorporates two prohibited labors causes liability for both. The Gemara concludes: Indeed, it is difficult according to both opinions. Rav Yosef raised an objection to the opinion of Rabba from what is taught in the following baraita: One who weeds in proximity to diverse kinds of seeds, or covers with earth the exposed roots of diverse kinds, is flogged for transgressing the prohibition against diverse kinds, i.e., tending different species of crops in one area of the same field, as it is stated: “You shall not sow your field with two kinds of seed” (Leviticus 19:19). Rabbi Akiva says: Even one who maintains in his field a mixture of species that he could have uprooted is flogged for violating the prohibition against diverse kinds of seeds. Rav Yosef explains: Granted, according to my opinion, that I say that one who weeds on Shabbat is forewarned for the prohibited labor of sowing, this is the reason he is liable to be punished with flogging for weeding diverse seeds: Sowing diverse kinds is prohibited. But according to you, who said that one who weeds on Shabbat is forewarned for plowing, why is one liable to be flogged for weeding in proximity to diverse kinds? Is plowing prohibited in connection with diverse kinds? At the time of plowing, there is no mixture of different species of crops, so plowing cannot be prohibited in this case. Rabba said to him: According to my opinion, one who weeds a field of diverse kinds is flogged not because he is guilty of plowing, but for violating the prohibition against maintaining a mixture of species in his field. The Gemara objects: However, from the fact that it teaches in the latter clause of the baraita that Rabbi Akiva says: Even one who maintains in his field a mixture of species is liable to be flogged, it may be inferred that according to the anonymous first tanna, the liability for weeding is not for maintaining diverse kinds, but for performing some other prohibited labor. The Gemara rejects this opinion: In fact, the entire baraita reflects the opinion of Rabbi Akiva, and it is stated in the style of what is the reason. The baraita should be understood as follows: What is the reason that one who weeds and one who covers the exposed roots of diverse kinds with earth is flogged? He is flogged for maintaining diverse kinds in his field, as Rabbi Akiva says: Even one who maintains in his field a mixture of species is flogged. With regard to Rabbi Akiva’s opinion, the Gemara asks: What is the reason for Rabbi Akiva’s opinion? How did he derive this prohibition from the verses? The Gemara answers: As it is taught in a baraita: “You shall not sow your field with mingled seed” (Leviticus 19:19). I have derived from this verse that only sowing diverse kinds is prohibited. From where is it derived that maintaining diverse kinds, which does not involve any positive action, is also prohibited? The verse states: “Diverse kinds, you shall not sow your field with mingled seed” (Leviticus 19:19). The prohibition against planting different species of a crop in one area of the same field is preceded in the verse by the prohibition against crossbreeding livestock: “You shall not let your cattle gender with a diverse kind.” A slight change in punctuation yields the phrase: Diverse kinds in your field, you shall not, indicating that merely preserving diverse kinds in one’s field is prohibited. § The Gemara returns to the original topic of discussion: We learned in the mishna: One may irrigate a field that requires irrigation on the intermediate days of a Festival as well as during the Sabbatical Year. The Gemara asks: Granted, with regard to the intermediate days of a Festival, where the prohibition against irrigation is due to the mandate to avoid excessive exertion on the Festival, in a case of considerable loss, the Sages permitted one to exert himself. However, during the Sabbatical Year, both according to the one who said that one who waters is liable due to the prohibition against sowing, and according to the one who said that one is liable due to the prohibition against plowing, are sowing and plowing permitted during the Sabbatical Year? How can these actions be permitted when the Torah explicitly renders prohibited working the land during the Sabbatical Year? Abaye said: The mishna is referring to the Sabbatical Year in the present time, when its prohibitions are only by rabbinic decree, and it is in accordance with the opinion of Rabbi Yehuda HaNasi. As it is taught in a baraita that Rabbi Yehuda HaNasi says: When the verse states: “And this is the manner of the release, every creditor will release that which he has lent to his neighbor” (Deuteronomy 15:2), the verse speaks of two releases: One is the release of land, that one must refrain from working the land, and the other is the release of money, that one must refrain from collecting debts.

Nafka mina #3:

Is Rava's opinion that usually there are toldos, and the passuk is teaching that these are the exceptions (Mahari Katz) or are there usually no toldos, and the passuk is teaching that these are the exceptions (Tosfos).

תָּנָא: הִגִּיהַּ אוֹת אַחַת — חַיָּיב. הַשְׁתָּא כָּתַב אוֹת אַחַת — פָּטוּר, הִגִּיהַּ אוֹת אַחַת חַיָּיב?! אָמַר רַב שֵׁשֶׁת: הָכָא בְּמַאי עָסְקִינַן — כְּגוֹן שֶׁנְּטָלוֹ לְגַגּוֹ שֶׁל חֵי״ת וַעֲשָׂאוֹ שְׁנֵי זַיְינִין. רָבָא אָמַר: כְּגוֹן שֶׁנְּטָלוֹ לְתָגוֹ שֶׁל דָּלֶ"ת וַעֲשָׂאוֹ רֵי״שׁ.

We learned in the mishna: If one wrote only a single letter, even if it was adjacent to other preexisting writing, he is exempt. The Gemara asks: Who is the tanna whose opinion is cited in the mishna? Rava bar Rav Huna said: This halakha is not in accordance with the opinion of Rabbi Eliezer, as if it were in accordance with the opinion of Rabbi Eliezer, didn’t he say: One who adds a single thread to a previously woven fabric is liable for weaving? In his opinion, although a single thread or letter is insignificant in and of itself, one is liable because adding even a small measure to existing material is significant.
מתני' (דף קד:) הכותב שתי אותיות בהעלם אחד חייב כתב בדיו בסם ובסקרא בקומוס ובקנקנתום ובכל דבר שהוא רושם על שני כותלי הבית על שני לוחי פנקס והן נהגין זה עם זה חייב.

רן בדפי הריף ד’’ה גרסינן

וכתוב בחדושי הרשב"א דמהא שמעי' דבכה"ג לא מיקרי חק תוכות שאינו אלא כמפריד בין שני אותיות דבוקות

ול"נ דאין מכאן ראיה דלגבי שבת ליכא קפידא בין חק תוכות לחק יריכות דכל היכא דהוי מלאכת מחשבת מיחייב שהרי אפי' מוחק על מנת לכתוב חייב אבל במידי דבעינן כתיבה [דלחזי כתיבה] כי האי גוונא אין לנו:

(כה) כל אות שהיא כתובה שלא כתקנה ואין צורתה עליה כגון נגע רגל האל"ף בגג האל"ף או פני האל"ף בפנים בגג שתחתי' או שהיה רגל הה"א או רגל הקו"ף נוגעים או שהיתה אות אחת חלוקה לשתי אותיות כגון צד"י שכתב יו"ד נו"ן או שי"ן שכתב עי"ן יו"ד או חי"ת שני זייני"ן ואחר שכתב לפניו חזר ותקנם הוי שלא כסדרן ופסולין

(25) Any letter that's written in an improper way and it doesn't have its normal form, for example, the "foot" of an "א" touched the "roof" of the "א", or the inner "face" of the "א" [touched] the bottom "roof", or the "foot" of a "ה" or the "foot" of a "ק" touched, or if one letter was split into two letters, for example a "צ" that was written as "נ" "י", or a "ש" that was written as "ע" י", or a "ח" [that was written] as two "ז"s, and after he proceeded writing, he went back and fixed them, it is as if it was written out of order and it is invalid. But, to separate attached letters — after he proceeded writing — is acceptable, because since the letter had its normal form, when it's separated from its friend it's not as if it was written [right then]. And so too is the law that if the small "י" that's on an "א" and a "ש" and a "ע", and the "foot" of a "ת" was not touching the body of the letter, and a child who's neither a genius nor a simpleton recognizes [the letter], that even though he proceeded writing, he is able to go back and fix it because since the normal form of the letter was recognizable it's not considered written out of order. And there are those who say that so too is the law if the "branch" on the top of a "ח" it not touching this to that, but the separation is not clearly recognizable, that even though a child reads it as two "ז" it's permitted to attach them.

אור זרוע א׳׳ח סי׳ ר׳׳ז

לפי עניית דעתי ניראה דהני דחק תוכות לאו כתיבה הוא – תולדה דכתיבה הוי. וכי האי גוונא כתב תוס׳ בכורות כה ע׳׳א.

Rashba: Removing top of ches is a melacha of kosev on shabbos, and in Kol HaTorah Kulah, but not chack tochos.

Ran: In kol hatorah kulah removing the top of a ches is chack tochos, and on shabbos you are chayav for meleches machsheves.

-S"A paskins like Ran.

Or Zarua: It's a toldah of ksivah.

Nafkah Minah #4:

Whether removing top of ches is a toldah or an av of kesivah.