Coherent systems of genus 0 II: Existence results for k\ge3
  In this paper we continue the investigation of coherent systems of type (n,d,k) on the projective line which are stable with respect to some value of the parameter \alpha. We work mainly with k<n and obtain existence results for arbitrary k in certain cases, together with complete results for k=3. Our methods involve the use of the "flips" which occur at critical values of the parameter. 
H. Lange and P. E. Newstead