procedure vpositive(var v: vector);
var
  n: integer;
begin { vpositive }
  for n:=0 to vdim-1 do with v[n] do begin
    if u.si<0 then writeln('vpositive: argument out of range')
    else if l.si<0 then l.si:=0;
  end;
end { vpositive };