Jianmin Xing and  Rufeng Xing,  Relative Injective Modules and Relative Flat Modules.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    February 2014, vol. 86(2). 365 - 372
    [viewed 19 April 2024]. Available from: https://publications.waset.org/pdf/9997594.