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- Sun Sook Jin, Yang-Hi Lee
- Adv. Fuzzy Systems
- 2011

- Sun Sook Jin, Yang-Hi Lee
- 2014

and Applied Analysis 3 is Cauchy. If each Cauchy sequence is convergent, then the fuzzy norm is said to be complete, and the fuzzy normed space is called a fuzzy Banach space. Let X,N be a fuzzy normed space and Y,N ′ a fuzzy Banach space. For a given mapping f : X → Y , we use the abbreviation Df ( x, y ) : f ( 2x y ) f ( 2x − y 2f x − fx y − fx − y − 2f… (More)

- Sun Sook Jin, Yang-Hi Lee
- Int. J. Math. Mathematical Sciences
- 2011

A classical question in the theory of functional equations is “when is it true that a mapping, which approximately satisfies a functional equation, must be somehow close to an exact solution of the equation?” Such a problem, called a stability problem of the functional equation, was formulated by Ulam 1 in 1940. In the next year, Hyers 2 gave a partial… (More)

- Yang-Hi Lee, Soon-Mo Jung
- Adv. Fuzzy Systems
- 2012

- SunSook Jin, Yang-Hi Lee, +4 authors YANG-HI LEE
- 2012

In this paper, we investigate a fuzzy version of stability for the functional equation 2f (x + y) + f (x − y) + f (y − x) − 3f (x) − f (−x) − 3f (y) − f (−y) = 0 in the sense of M. Mirmostafaee and M. S. Moslehian.

- Sun Sook Jin, Yang-Hi Lee
- 2011

In this paper, we investigate a fuzzy version of stability for the functional equation f (x + y + z) − f (x + y) − f (y + z) − f (x + z) + f (x) + f (y) + f (z) = 0 in the sense of Mirmostafaee and Moslehian.

- Sun Sook Jin, Yang-Hi Lee
- 2012

In this paper, we prove the stability in random normed spaces via fixed point method for the functional equation f (x + 2y) − 2f (x + y) + 2f (x − y) − f (x − 2y) = 0.

- Sun Sook Jin, Yang-Hi Lee
- 2014

tributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract In this paper, we investigate the stability problems for a functional equation f (ax + y) + af (x − y) − a 2 +3a 2 f (x) − a(a−1) 2 f (−x) − f (y) − af (−y) = 0 by using… (More)

- Kil-Woung Jun, Yang-Hi Lee, Juri Lee, Patricia Wong
- 2008

- Sun Sook Jin, Yang-Hi Lee, Sun-Sook Jin
- 2013

tributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract In this paper, we investigate a fuzzy version of stability for the functional equation f ⎛ ⎝ n j=1 x j