“…Cholewa [5] noticed that the theorem of Skof is still true if the relevant domain 320 Harin Lee, Jae Young Cha, Min Woo Cho & Myungjun Kwon E 1 is replaced by an Abelian group. The stability problems of various functional equations have been extensively investigated by a number of authors (see [1,3,4,6,9,10,11,12,13,15,17,18,19,20,21,24,25]). Definition 1.1.…”