AN 5.161, AN 5.162: I solved a few mysteries this week, regarding mudita and upekkha as part of 4 brahma viharas

4👑☸ Cattāri Ariya-saccaṃ 四聖諦

4👑☸ → AN 5.161      AN   DN   KN   MN   SN   (⤴)

AN 5.161

• AN 5.160 Du-p-paṭi-vinodaya
• AN 5.161 Paṭhama-āghāta-paṭi-vinaya
  • (1. Mettā🤝🤗: friendly-kindness)
  • (2. Karuṇā👐😊: Compassion)
  • (3. Upekkhā🛆👁️: Equanimous-observation)
  • (4. Forget and ignore)
  • (5. STED kamma-s-sakka: karma’s-owner)
• AN 5.162 Dutiya-āghāta-paṭi-vinaya
  • (1. body=impure, speech=pure)
  • (2. body=pure, speech=impure)
  • (3. body=impure, speech=impure, clarity = yes)
  • (4. body=impure, speech=impure, clarity = no)
  • (4. body=pure, speech=pure, clarity = yes)

Why is mudita missing from AN 5.161? It jumps from karuna right to upekkha.

It's because the entirety of the next sutta, AN 5.161 is completely dealing with mudita. This is an interesting feature of EBT, where it often doesn't tell you things in such explicit wording like you would expect in a college textbook or legal document. You have to read and examine very carefully to notice important details like this. If you do a text search for "mudit" (mudita and conjugations) in those 3 suttas, it doesn't appear! But it's omission from AN 5.161 and the theme from the following sutta makes it incontrovertible that mudita as a brahma-vihara is the topic.

Here, I did a detailed comphrensive research on mudita, piti, pamojja (conjugated form of mudita). For mudita, I searched "mudit" in DPR and looked at EVERY SINGLE SUTTA occurrence of that term. The results are here:
http://www.lucid24.org/sted/7sb/4piti/book/index.html

mudita/pamojja, much like "sukha" in 7sb☀️ = satta bojjh-aṅga , are shadow factors. They don't officially appear in the list of 7, but if you have passaddhi/pacification, then sukha is there like a shadow (unless samadhi is 4th jhana or higher). Similarly, piti-sambojjhanga has mudita/pamojja joined like a twin or shadow.  

Mudita is not ordinary gladness/enjoyment. It's altruistic-mirth that delights in virtue, that delights in Dharma that leads to viraga, nirodha, nirvana. 

Mystery of mudita in 4bv solved

So the question I asked on the forums earlier, now as its answer. I noted that in the EBT, and Vimt. (vimuttimagga), mudita as one of 4bv ☮️= 4 Brahma vihāras , only talked about happiness at noticing virtuous qualties in onesself and others. Whereas Vism. seems to go off on a tangent and talk about non-jealousy.

AN 5.161 and AN 5.162 gives the answer. Notice both suttas are spoken by Sariputta, not the Buddha. Often late Theravada ideas, you'll see they try to pin the credit (or blame?) on Sariputta, for ideas that are not in the EBT. Especially for the 5th factor in AN 5.192, where the person one has resentment towards has no blemish, but one has resentment towards them. That's the 'jealousy' angle the Vism. talks about.

Mystery solved: of  4bv Upekkha relationship to 'kamma-saka: it's karma, sucka!'

in AN 5.191, since mudita is omitted and treated in detail in AN 5.192, then the last two factors of AN 5.191, 'forget and ignore', and 'kamma-saka', are clearly expanding on upekkha.  Again, I think this is an idea from late Theravada, due to it being spoken by Sariputta. In the other sutta references where the Buddha talks about it, it's not connected to upekkha as a 4bv, or upekkha in general.
http://www.lucid24.org/tped/k/kamma/book/index.html