On a joint $(m, (q_1, ..., q_d))$-partial isometries and a joint   $m$-invertible $d$-tuple of operators on a Hilbert space
  The aim of the present paper is, firstly we study the concepts of (m, (q_1, ..., q_d))- partial isometries on a Hilbert space, secondly, we introduce the notion of m- invertibility of tuples of operators as a natural generalization of the m-invertibility in single variable operators. 
Ould Ahmed Mahmoud Sid Ahmed
math.FA math.OA