Two types of multidimensional processes are defined. The first of these generalizes a univariate IFRA process due to Ross and relates to a multivariate concept of IFRA due to Esary and Marshall. The second of these relates to a multivariate concept of IFRA due to the present authors.
"Multidimensional IFRA Processes." Ann. Probab. 9 (1) 162 - 166, February, 1981. https://doi.org/10.1214/aop/1176994518