I collaborated with Bob Clapp and Jon Claerbout on developing recursive preconditioning for missing data interpolation problems Clapp et al. (1997); Fomel et al. (1997) and with Paul Sava, James Rickett, and Jon Claerbout on developing the helical version of the Wilson-Burg method Sava et al. (1998); Sava and Fomel (1999). For the latter, we owe a great deal to John Burg. I would like to thank him and Francis Muir for many useful and stimulating discussions.