• Bulletin of the Korean Mathematical Society
• /
• v.51 no.2
• /
• pp.501-510
• /
• 2014

We characterize hypergeneralized k-projectors (i.e., $A^k=A^{\dag}$). Also, some representation for the Moore-Penrose inverse of a linear combination of hypergeneralized k-projectors is found and the invertibility for some linear combinations of commuting hypergeneralized k-projectors is considered.

• East Asian mathematical journal
• /
• v.22 no.2
• /
• pp.151-162
• /
• 2006

In this paper two coincidence point theorems in complete metric spaces for two pairs of single and multi-valued mappings have been established.

• Bulletin of the Korean Mathematical Society
• /
• v.29 no.2
• /
• pp.221-226
• /
• 1992

The involutions in a left Artinian ring A with identity are investigated. Those left Artinian rings A for which 2 is a unit in A and the set of involutions in A forms a finite abelian group are characterized by the number of involutions in A.

• Proceedings of the KOR-KST Conference
• /
• 2007.05a
• /
• pp.118-127
• /
• 2007

• Journal of the Chungcheong Mathematical Society
• /
• v.14 no.1
• /
• pp.105-111
• /
• 2001

The purpose of this paper is to give a new generalization of the well-known common fixed point theorem due to Markov-Kakutani in general settings.

• Communications of the Korean Mathematical Society
• /
• v.16 no.2
• /
• pp.235-241
• /
• 2001

In this paper we study some properties of he joint Weyl and Browder spectra for the slightly larger classes containing doubly commuting n-tuples of hyponormal operators.

• Bulletin of the Korean Mathematical Society
• /
• v.37 no.1
• /
• pp.53-62
• /
• 2000

In this paper we explore relations between joint Weyl and Browder spectra. Also, we give a spectral characterization of the Taylor-Browder spectrum for special classes of doubly commuting n-tuples of operators and then give a partial answer to Duggal's question.

• Journal of the Korean Mathematical Society
• /
• v.44 no.4
• /
• pp.855-861
• /
• 2007

Let A and B be commuting bounded linear operators on a Hilbert space. In this paper, we study spectral area estimates for norms of $A^*B-BA^*$ when A is subnormal or p-hyponormal.

• Communications of the Korean Mathematical Society
• /
• v.34 no.2
• /
• pp.533-542
• /
• 2019

We study commutants of Toeplitz operators acting on the Dirichlet space of the unit disk and prove that an operator in the Toeplitz algebra commuting with a Toeplitz operator with a nonconstant polynomial symbol must be a Toeplitz operator with an analytic symbol.

• Communications of the Korean Mathematical Society
• /
• v.34 no.4
• /
• pp.1099-1104
• /
• 2019

In [1], Ali and Dar proved the ${\ast}$-version of classical theorem due to Posner [15, Theorem] with involution of the second kind. The main objective of this paper is to improve the above mentioned result without the condition of the second kind involution. Moreover, a related result has been discussed.