When writing a Torah, each letter must be written according to a specific shape / form that is defined for each letter. Certain letters contain tagin (crowns). Are these tagin considered part of the definition of the letter form / shape itself? When a sofer writes one of the letters that have the tagin, is he required to put those tagin there because the rules of how the letter must be drawn include instructions and requirements for drawing it with the tagin?
Applications of this question:
1 - If the tagin are part of the definition of the letter and the Sofer does not include them, would that disqualify the Torah, since he is not writing the shape of the letters correctly?
2 - In the written Torah there are 2 upside down nuns - one before Bamidbar 10:35 and one after Bamidbar 10:36.
Tikkun Sofrim (Tel Aviv 57725) shows the upside down nuns with the tagin ("crowns") on top. If the tagin are included within the definition of the shape of the letter, then if the nun is turned upside down, shouldn't the tagin be on the bottom rather than the top.
Note: Thanks to DoubleAA for pointing out that in the drawing it is backwards, not upside down. There may be different permissible interpretations on how the Nun is allowed to be drawn, here. I know that in many Sifrei Torah, I have seen it upside down, but I don't know if the tagin are drawn on top or on the bottom.