theorem
  s/.3 = S-max L~s & s/.3 = E-min L~s
proof
  consider D such that
A1: s = SpStSeq D by Def2;
A2: s/.3 = SE-corner D by A1,Th37;
  hence s/.3 = S-max L~s by A1,Th81;
  thus thesis by A1,A2,Th78;
end;
