COMMENT: The WC form has a prefix of unknown origin; despite this, and the lack of the expected palatalisation (*-x́ʷǝ would be rather expected), there can be no doubt in the common origin of the EC and WC forms. The rules of palatalisation are violated in WC numerals (cf. also EC *ƛHĕ 'three' : WC *ʎ:V), possibly because of original Ablaut.
See Trubetzkoy 1922, 239, 243; 1930, 274-275; Абдоков 1983, 155.
