Responsa על מכות 39:2

Regarding one who shaves with a razor around the neck, is there somewhat of a transgression in doing so, or is it completely permitted?¹Although the Talmud (Makkot 20a:10) mentions that there are five parts of the beard that are forbidden to be shaved with a razor, it is unclear what those five are. Rabbeinu Chananel is said to have included the Adam's apple (see Tur Yoreh Deah 181:11), this is also the opinion of Sefer Mitzvot Gadol, Negative Commandments 58. Rabbeinu Yonah Gerondi (cited in Beit Yosef Yoreh Deah 181) writes that "all the rabbis of France" would be careful not to shave their throats, even though it is not forbidden biblically.

I also asked [in my dream] regarding those who destroy their beards while leaving one hair on each of the corners¹i.e, the five parts of the beard that are not allowed to be shaved with a razor, see Makkot 20a.10 . See Siman 50, and notes there. Perhaps the style of cutting in this question is the same as the one referred to there, with a single line of hair remaining on the edge of the beard. Maimonides requires forty hairs to remain on each of the corners (Mishneh Torah, Foreign Worship 12:6), but see Beit Yosef Yoreh Deah 181 for discussion of manuscripts that have 'four' instead of 'forty', and compare Rashi on Makkot 20a:10 where the minimal amount is much greater.. Afterwards, they cut those remaining hairs with scissors, and it seems as if they had shaved their whole face with a razor²On the issue of using the blade of scissors in place of a razor, see Mishneh Torah, ibid., who permits scissors unconditionally, and Tosafot on Shevuot 2b:12. I asked whether this was a grave transgression, in which case I should protest as much as possible, or whether it is not so grave, and not worth fighting over³Compare Hagahot Rabbeinu Peretz on Sefer Mitzvot Katan 70, who calls those who leave one hair on their beards 'destructive infants' (בנים משחיתים).