[1] Artikis T.: 
On the unimodality and self-decomposability of certain transformed distributions. Bull. Greek Math. Soc. 20 (1979), 3-9. 
MR 0642426 | 
Zbl 0451.60022 
[2] Ibragimov I. A.: 
On the composition of unimodal distributions. Theor. Probability Appl. 1 (1956) 255-260. 
MR 0087249 | 
Zbl 0073.12501 
[4] Medgyessy P.: 
On a new class of infinitely divisible distribution functions and related topics. Studia Scient. Math. Hung. 2 (1967) 441-446. 
MR 0222929 
[5] O'Connoг T.: 
Infinitely divisible distributions with unimodal Levy spectral functions. Ann. Probability 7 (1979), 494-499. 
MR 0528326 
[6] Sakovic G. N.: 
The characteristic functions of concave distributions. Theoг. Verojatnost. i. Mat Statist. Vyp. 6 (1972). 103-108. 
MR 0309168