This particle triggerssoft mutation, except for on words beginning with ⟨rh⟩ and ⟨ll⟩, of anything substantival, namely nouns, adjectives, numerals and verbal nouns used substantivally.
It triggers no mutation on anything verbal, which in practice means verbal nouns used verbally.
This particle triggersnasal mutation. Before ⟨p⟩, ⟨b⟩ and sometimes ⟨m⟩, it becomesym and before ⟨c⟩ and ⟨g⟩, it becomesyng. In certain informal contexts or dialects, it may triggersoft or no mutation at all.
R. J. Thomas, G. A. Bevan, P. J. Donovan, A. Hawke et al., editors (1950–present), “yn”, inGeiriadur Prifysgol Cymru Online (in Welsh), University of Wales Centre for Advanced Welsh & Celtic Studies
Jacob Poole (d. 1827) (before 1828) William Barnes, editor,A Glossary, With some Pieces of Verse, of the old Dialect of the English Colony in the Baronies of Forth and Bargy, County of Wexford, Ireland, London: J. Russell Smith, published1867,page114
