Sukhwinder Singh Billing and  Sushma Gupta and  Sukhjit Singh Dhaliwal,  An Application of Differential Subordination to Analytic Functions.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    July 2009, vol. 31(7). 551 - 553
    [viewed 18 November 2019]. Available from: https://publications.waset.org/pdf/15126.