Bibliographical noteFunding Information:
I thank A. Stipsicz for many stimulating discussions. I also wish to thank K. F. Liu, F. Luo, Y. Matsumoto, B. Ozbagci, T. Pantev, I. Smith, G. Tian, and S. T. Yau for their interest in this work. I am grateful to the referee, whose many suggestions greatly improved the quality of the presentation. My work was partially supported by National Science Foundation grant number DM-9975469.