Geometry of generic Moishezon twistor spaces on 4CP^2, II: degenerate cases

Abstract

We continue to study twistor spaces on the connected sum of four complex projective planes, whose anticanonical map is of degree two over the image. In particular, we determine the defining equation of the branch divisor of the anticanonical map in an explicit form. Together with previous two articles (arXiv:1009.3153 and arXiv:0705.0060), this completes explicit description of all such twistor spaces.