Slice Spirallike Functions over Quaternions

In this paper, we study the analogue of spirallikeness for slice regular functions of one quaternionic variable. In particular, we introduce the concept of slice & gamma;\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\gamma $$\end{document}-spirallike functions of order & alpha;\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha $$\end{document} and investigate its geometric function theory, such as coefficient estimates, growth and covering theorems. As a byproduct, the Robertson's result concerning the radii of starlikeness for holomorphic spirallike functions is generalized into slice regular functions by a very concise method, but new even for the classical case.