Many-to-one: accent marks, e.g. umlauts One-glyph-to-many-unicode-characters: ligatures, e.g. "ff", "fi".
I don’t see how these two cases are different. An accented glyph like ⟨ɑ̃⟩ is made up of two Unicode characters, ɑ+◌̃ (U+0251 U+0303); similarly a ligated glyph like ⟨fi⟩ is made up of the two Unicode characters f+i (U+0066 U+0069).
Regards, Brad
