theorem
  s/.4 = S-min L~s & s/.4 = W-min L~s
proof
  consider D such that
A1: s = SpStSeq D by Def2;
A2: s/.4 = SW-corner D by A1,Th38;
  hence s/.4 = S-min L~s by A1,Th80;
  thus thesis by A1,A2,Th74;
end;
