Haldeman's Variations on a Theme: Forever War and Forever Peace
Erlich, Richard D. "The Forever War (1972-75, 1975/76, 1997) and Forever Peace (1997): Haldeman's Variations on a Theme by Haldeman." In Flashes of the Fantastic (Selected Proceedings of the 19th Annual International Conference on the Fantastic in the Arts). Ed. David Ketterer. Westport, CT: Greenwood Press, 2004: 109-31; ch. 9.
See especially for bibliographic background on the differing versions of The Forever War.