theorem
  a <= b & b <= c implies a <= c
  proof
    assume that
A1: a <= b and
A2: b <= c;
    for i be Nat st i in Seg n holds a.i <= c.i
    proof
      let i be Nat;
      assume i in Seg n;
      then a.i <= b.i & b.i <= c.i by A1,A2;
      hence thesis by XXREAL_0:2;
    end;
    hence thesis;
  end;
