In this short communication, we first introduce inner straight line G(
(x,y)) on the subset G in the Euclidean space R-n, and define the conc
ept of the weakly quasi-convex fuzzy sets. Second, we will give a weak
equivalent condition that a fuzzy closed set is a convex fuzzy set. (
C) 1998 Elsevier Science B.V. All rights reserved.