Returns the set of IPA symbols that are precomposed (decomposable)
		chars. These should not be decomposed during string normalisation,
		because they will not be recognised otherwise.

		In IPA 2015 there is only one precomposed character: ç, the voiceless
		palatal fricative.

def get_nfc_chars(self):
		"""
		Returns the set of IPA symbols that are precomposed (decomposable)
		chars. These should not be decomposed during string normalisation,
		because they will not be recognised otherwise.

		In IPA 2015 there is only one precomposed character: ç, the voiceless
		palatal fricative.
		"""
		ex = []

		for char in self.ipa.keys():
			if len(char) == 1:
				decomp = unicodedata.normalize('NFD', char)
				if len(decomp) == 2:
					ex.append(char)

		return set(ex)