%
% initiate the reverse time lookup
%
 snap "xact*" xactseed
 File.FoldPrev
"xsubx" log)(
 0 !Xact
 any?
 {
  fileroot -4 left
  !Xact
 } if
 _Xact
"xsubb" log)(
 nonzero
 dup
 {
%
% insure not below xact of first subject encounter
%
  _Xact _Xact.Limit lt
  {
"xsubc" log)(
   pop false
  } if
 } if
"xsubd" log)(
%
% stack: have-xact
%