reserve x for Real;

theorem Th4:
  for n be Nat st x >= 0 & n <> 0 holds (n-root x) |^ n = x
proof
  let n be Nat;
  assume that
A1: x >= 0 and
A2: n <> 0;
  n >= 0+1 by A2,NAT_1:13;
  hence thesis by A1,POWER:4;
end;
