What is the definition of a Mamzer?
Ramban (according to Shimon ha'Teimani, in Yevamos 49a): A Mamzer 1 is either a child born from an Ervah of Chayvei Kerisus 2 or the child of a Mamzer.
Yevamos 49a (according to R. Akiva) #1: A Mamzer is a child born (even) from Chayvei La'avin 3 (or the child of a Mamzer).
Yevamos 49a (according to R Yehoshua) #2: A Mamzer is a child born from Chayvei Misas Beis Din (or the child of a Mamzer).
Kidushin, 73a: "Mamzer" implies Vadai Mamzer - but a Safek Mamzer 4 is permitted, 5 and by the same token, "K'hal Hashem" implies Kahal Vadai - but a Mamzer is permitted to marry into a Safek Kahal. 6
Ramban and Targum Yonasan: Which is the acronym of 'Mum Zar' (a blemish that is to be found among other nations ? Targum Yonasan). See Ramban.
Yevamos 49a: Some say that R. Akiva discusses only Chayvei La'avim of She'er (blood relatives), others, even not of She'er, and some say even the chilkd of Chayvei Asei. All opinions agree however, that there is no Mamzer from Isurei Kehunah.
See Torah Temimah, note 17.
There is nothing in the Pasuk that implies Vaday but not Safek, and the D'rashah can only be based on the principlke 'S'feika d'Oraysa min ha'Torah le'Kula' - like the opinion of the Rambam.
What is the Din regarding a Mamzeres?
Yevamos, 77a: The very word 'Mamzer' - acronym 'Mum Zar' (a blemish of Zarus) - incorporates both a man and a woman. 1
See Torah Temimah, note 18.
Why does the Torah insert the (otherwise superfluous) word "Lo Yavo lo bi'Kehal Hashem"?
Yerushalmi Kidushin, 3:12: To teach us that in a case of a Mamzeres or Nesinah to a Yisrael, the cild goes after the Pasul - and not after the father. 1
See Torah Temimah, note 23.
Why is a Mamzer, who did nothing wrong, forbidden to enter the K'hal Hashem?
Why does the Torah write - in connection with Pesulei Kahal - "bi'Kehal Hashem" five times?
Kidushin, 73a: 1. Regarding K'hal Kohanim; 2. regarding K'hal Levi'im; 3. regarding K'hal Yisre'elim; 4. to permit a Mamzer to marry a Shesuki 1 (a Safek Mamzer); 5. to permit a Shesuki to marry a Yisrael. 2 And the fact that there is no Pasuk to incorporate a Kahal of Geirim teaches us that 'K'hal Geirim Lo Ikri Kahal'.