Akbar Paad - Academic Member, Department of Mathematics, University of Bojnord, Bojnord, Iran,
Rajab Ali Borzooei - Academic Member, Department of Mathematics, Shahid Beheshti University, Tehran, Iran,

In this paper, we introduced the notion of n-fold obstinate BL- algebras and we stated and proved some theorems, which determine the relationship between this notion and other types of logical algebraic structures. It was an open problem in [7] that we answered it. Moreover, we prove that a BL-algebra L is an n-fold obstinate BL-algebra if and only if L is an MV–algebra and n-fold integral BL-algebra.

BL-algebra, n-fold obstinate BL-algebra and n-fold integral BL-algebra