reserve x for set;
reserve a, b, c for Real;
reserve m, n, m1, m2 for Nat;
reserve k, l for Integer;
reserve p, q for Rational;
reserve s1, s2 for Real_Sequence;

theorem Th21:
  a>=0 implies 1 -Root a = a
proof
  assume
A1: a>=0;
  a |^ 1 = a GeoSeq.(0+1) by Def1
    .= a GeoSeq.0 * a by Th3
    .= 1*a by Th3
    .= a;
  hence thesis by A1,Th19;
end;
