diff --git a/🔰 Grammar/Obligation.md b/🔰 Grammar/Obligation.md
index 57c503e..3dc20eb 100644
--- a/🔰 Grammar/Obligation.md	
+++ b/🔰 Grammar/Obligation.md	
@@ -26,17 +26,28 @@ Can be used as わけはいかない or わけにはいきません.
 > {本当|ほんとう}に飲み会に行く==わけにはいかない==よ。
 > There's really no way I can go to the afterwork.
 
-## ずにはいられない
+## なくてもいい
 
-Means "can't help but do something".
-Made with a verb in the negative form (ない) without the ない ending and adding ずにはいられない. 
+Means "don't have to". Used with a verb in the negative form (ない), appending なくてもいい.
+Can also be used as なくていい.
 
 > [!info] Example
-> {悲|かな}しいのでアイスクリーム食べ==ずには入れれない==。
-> I'm sad so I can't help but eat ice cream.
+> 今日はレストランで{手伝|て|つ}わ==なくてもいい==。
+> You don't have to help out at the restaurant today (it's okay if you don't help at the restaurant today).
+
+## てからでないと
+
+Means "must first do". The second part becomes possible after the first one.
+Used with a verb in て form, with からでないと or からでないければ.
+
+> [!info] Example
+> {払|はら}==ってからでないと=={入|はい}るができること。
+> You can enter only after paying.
 
 ## こと as "should do"
 
+### こと
+
 <div class="usage">
 <div class="left">
 	<p><span class="box">V (dictionary)</span></p>
@@ -51,7 +62,16 @@ Means "should do". Mostly used to set rules.
 > ここに{車|くるま}を{止|と}めない==こと==です。
 > Don't park your car here.
 
-## ことはない
+### ことになっている
+
+This form is used to express rules or expectations.
+Used with dictionary (る) and negative (ない) form of verbs.
+
+> [!info] Examples
+> {指|ゆび}で食べない==ことになっている==。
+> You're not supposed to eat with your fingers.
+
+### ことはない
 
 This has two meanings:
 * it is not necessary to
@@ -63,57 +83,19 @@ Used with a verb in the dictionary form.
 > {走|はし}る==ことはない==。まだ{時間|じかん}がある。
 > There's no need to run. There's still time.
 
-## ことになっている
+## 必ず
 
-This form is used to express rules or expectations.
-Used with dictionary (る) and negative (ない) form of verbs.
-
-> [!info] Examples
-> {指|ゆび}で食べない==ことになっている==。
-> You're not supposed to eat with your fingers.
-
-## Must
-
-### なくちゃ・なきゃ
-
-Only used on casual spoken conversations.
-This form is used with the negative form of a verb (ない), and adding なくちゃ and optionally one of the following ending: だめ, いけない, いけません, ならない, なりません.
-
-なくちゃ is the shortened form of なくては.
-なきゃ is the shortened form of なければ.
+{必|かなら}ず means certainly, definitely. Expresses an obligation.
 
 > [!info] Example
-> {歯|は}を{磨|みが}か==なくちゃいけない==。
-> I must brush my teeth.
+> 明日の{授業|じゅ|ぎょう}==必ず==来てください。
+> Please be sure to attend tomorrow's class.
 
-### なくては「いけない・ならない」
-
-Also formed with the negative form of a verb.
-
-> [!info] Example
-> 今{遅|おそ}いね。{寝|ね}に行か==なくてはいけない==。
-> It's late now. I have to go to sleep.
-
-### なければ「いけない・ならない」
-
-Also formed with the negative form of a verb.
-
-> [!info] Example
-> {事務所|じむしょ}では{静|しず}かにし==なければならない==。
-> You have to be quiet in the office.
-
-### ないといけない
-
-Also formed with the negative form of a verb.
-In casual contexts, can be shortened as ないと.
-
-> [!info] Example
-> 今日は{勉強|べんきょう}し==ないといけない==。
-> I have to study today.
+## べき
 
 ### べきだ
 
-Means "should do", "must do".
+Means "should do", "must do". Compared to the [[Obligation - なければ・ないと]] forms and 必ず, it has a nuance of being less universally logical. It is defined by the speaker's own logic.
 Used with verbs.
 する can be used as するべき or すべき.
 
@@ -121,64 +103,6 @@ Used with verbs.
 > {来週|らいしゅう}{試験|しけん}があるので{勉強|べんきょう}す==べきです==。
 > There is an exam next week, so I should study.
 
-## てからでないと
-
-Means "must first do". The second part becomes possible after the first one.
-Used with a verb in て form, with からでないと or からでないければ.
-
-> [!info] Example
-> {払|はら}==ってからでないと=={入|はい}るができること。
-> You can enter only after paying.
-
-
-🛠🛠🛠🛠
-Todo: new notions!
-
-### Comparing いけない and ならない
-
-* ==いけない== is the standardly used form. It implies a subjective view, that it would be better to do something, to avoid negative consequences (eg: brushing one's teeth, eating well, etc).
-* ==ならない== is usually more formal or in written form. It implies a is more objective view, something that has to be done because there's no other way (eg: respecting the law, paying taxes, etc).
-
-### Comparing なくては, なければ and ないと
-
-なくては and なければ are generally interchangeable in speech. However:
-* ==なくては== is generally used when there is _no penalty_ for not complying.
-* ==なければ== is generally used when there _is a penalty_ for not complying.
-* ==ないと== is lighter and does not imply that there can or cannot be penalty. Its construction is based on the [[Conditional#と]] particle, and should be based on knowledge or experience.
-
-## Must not
-
-#### 「ちゃ・じゃ」「だめ・いけない・いけません」
-
-Only used on casual spoken conversations. いけません is a bit more formal.
-This form is used with a V-て, depending on the ending:
-* with て, ちゃ is used.
-* with で, じゃ is used.
-
-> [!info] Examples
-> その{花|はな}を食べ==ちゃだめ==。
-> Don't eat those flowers.
-> 
-> {花瓶|か|びん}の水を{飲|の}ん==じゃいけない==。
-> Don't drink the water of the flower vase.
-
-### てはいけない
-
-Used in a more formal or written manner. Used with a V-て.
-
-> [!info] Example
-> {鉄道|てつ|どう}に{歩|ある}い==てはいけません==。
-> Do not walk on the railroad.
-
-### なくてもいい
-
-Means "don't have to". Used with a verb in the negative form (ない), appending なくてもいい.
-Can also be used as なくていい.
-
-> [!info] Example
-> 今日はレストランで{手伝|て|つ}わ==なくてもいい==。
-> You don't have to help out at the restaurant today (it's okay if you don't help at the restaurant today).
-
 ### べきではない・べきじゃない
 
 The contrary of べきだ is べきではない・べきじゃない.
@@ -187,45 +111,23 @@ The contrary of べきだ is べきではない・べきじゃない.
 > {泥|どろ}を食べる==べきではない==。
 > You should not eat mud.
 
-
-
-
-
-## ても構わない
+## はずだ・はずがない
 
 <div class="usage">
 <div class="left">
-	<p><span class="box">V (て)</span></p>
-	<p><span class="box">い-Adj <strike>い</strike> くて</span></p>
-	<p><span class="box">な-Adj + で</span></p>
-	<p><span class="box">N + で</span></p>
+	<p><span class="box">V</span></p>
+	<p><span class="box">い-Adj</span></p>
+	<p><span class="box">な-Adj + な</span></p>
+	<p><span class="box">N + の</span></p>
 </div>
-	<p class="right">+ もかまわない・もかまいません</p>
+	<p class="right">+ はずだ ・ はずがない</p>
 </div>
 
-Means "it doesn't matter if", "I don't mind".
+はずだ means "it must/should be", while はずがない means "it cannot be". Has a nuance of being sure that it is something possible (or impossible).
 
-> [!info] Example
-> ここで{座|すわ}==っても構いません==か。
-> Would it be okay if I sit here?
+> [!info] Examples
+> {彼|かれ}は今日来る==はずだ==。
+> He should be coming today.
 > 
-> ==かまわない==よ。
-> I don't mind.
-
-
-
-
-
-
-# TODO
-
-## ないと
-
-
-
-
-
-must do; unless/if you don't ~
-
-https://jlptsensei.com/learn-japanese-grammar/%e3%81%aa%e3%81%84%e3%81%a8-naito-meaning/
-https://bunpro.jp/grammar_points/%E3%81%AA%E3%81%84%E3%81%A8
+> そんあ==はずがありません==。
+> This cannot be true.