procedure step (b:TStringGrid; i,j:integer);
BEGIN
  b.Cells[i,j]:=a[i+1,j+1];
  if b.Cells[i,j]=' ' then
     begin
       if (i>0) then
          begin
            if (b.Cells[i-1,j]='?')   then
               step(b,i-1,j);
            if (j>0)    then
               if (b.Cells[i-1,j-1]='?') then
                  step(b,i-1,j-1);
            if (j<s2-1) then
               if (b.Cells[i-1,j+1]='?') then
                  step(b,i-1,j+1)
          end;
       if (i<s1-1) then
          begin
            if (b.Cells[i+1,j]='?')then
               step(b,i+1,j);
            if (j>0)    then
               if (b.Cells[i+1,j-1]='?') then
                  step(b,i+1,j-1);
            if (j<s2-1) then
               if (b.Cells[i+1,j+1]='?') then
                  step(b,i+1,j+1)
          end;
       if (j>0) then
          if (b.Cells[i,j-1]='?')then
             step(b,i,j-1);
       if (j<s2-1)   then
          if (b.Cells[i,j+1]='?')   then
             step(b,i,j+1);
     end
END;