Look at this page to find why this happens: http://www.kervarker.org/fr/grammar_01_kemmadur.html
Perhaps I won't. I know about Breton mutation. See http://www.evertype.com/gram/bg.html
By "rare" I mean words without mutation of the leading consonnant. The same number above would be "kwec'h" without the mutation...
This is incorrect. *kwec'h does not occur; neither does *kwi. In fact, no words in kw- occur.
Typical breton dictionnaries will list the word only at K, and not at C'H
This is incorrect. For instance the 1200-page monolingual Breton dictionary published in 1995 gives them under C'H.
(in fact the prefered Breton sorting order generally orders C'H between K and L, and GW between W and X).
This is incorrect. Alphabetical order is A B C CH C'H D E F G H I J K L M N O P R S T U V W Y Z
X does not occur. GW is not a letter of its own.
The old alphabetical order was A B K D E F G H CH C'H I Y J L M N O P R S T U V W Z
Sometimes, as in Kervella's _Yezhadur bras ar brezhoneg_, GW was separated out between G and H (where it would fall anyway).
-- Michael Everson * * Everson Typography * * http://www.evertype.com

