Andrica, D., and N. Muşuroia. “Cones of Holomorphic Functions With Positive Real Part”. Anal. Numér. Théor. Approx., vol. 10, no. 2, Aug. 1981, pp. 133-9, https://ictp.acad.ro/jnaat/journal/article/view/1981-vol10-no2-art1.