theorem Th6:
  for N,n be Nat,seq be Real_Sequence of N holds
  (-seq).n = -seq.n
  proof
    let N,n be Nat,seq be Real_Sequence of N;
    reconsider m = n as Element of NAT by ORDINAL1:def 12;
A1: dom(-seq) = NAT by FUNCT_2:def 1;
    thus (-seq).n = (-seq)/.m
    .= -seq/.m by A1,VFUNCT_1:def 5
    .= -seq.n;
  end;
