Exact Solutions of Einstein's Field Equations

When,  in  1975,  two of the authors  (D.K. and H.S.) proposed  to change
their field of research back  to  the  subject of exact solutions of Einstein's
field  equations,  they  of course  felt  it  necessary  to make  a  careful  study
of  the  papers published  in  the meantime,  so as  to  avoid  duplication  of
known  results. A fairly comprehensive review or book on  the exact solu­
tions would have been a great help, but no such book was available. This
prompted  them  to ask  'Why  not  use  the  preparatory work we have  to
do in any case to write such a book?' After some discussion,  they agreed
to  go  ahead  with  this  idea,  and  then  they  looked  for  coauthors.  They
succeeded  in finding  two.