Harmonic Functions Starlike in the Unit Disk

Complex-valued harmonic functions that are univalent and sense-preserving in the unit disk D can be written in the form fshqg, where h and g are analytic in D. We give univalence criteria and sufficient coefficient conditions for normalized harmonic functions that are starlike of order a, 0Fa -1. These coefficient conditions are also shown to be necessary when h has negative and g has positive coefficients. These lead to extreme points and distortion bounds