.TLPREFACE.LPAlthough this Seventh Edition no longer bears their byline,Ken Thompson and Dennis Ritchie remain the fathersand preceptors of the.UXtime-sharing system.Many of the improvements here described bear their mark.Among many, many other people who have contributed tothe further flowering of\s-2UNIX\s0,we wish especially toacknowledge the contributions ofA. V. Aho,S. R. Bourne,L. L. Cherry,G. L. Chesson,S. I. Feldman,C. B. Haley,R. C. Haight,S. C. Johnson,M. E. Lesk,T. L. Lyon,L. E. McMahon,R. Morris,R. Muha,D. A. Nowitz,L. Wehr,andP. J. Weinberger.We appreciate also the effective advice and criticism ofT. A. Dolotta,A. G. Fraser,J. F. Maranzano,andJ. R. Mashey;and we remember the important work ofthe late Joseph F. Ossanna..sp 2.in 4iB. W. Kernighan.brM. D. McIlroy.in 0