theorem Th29:
  q>0 & n>0 implies ex r st q = r|^n
  proof
    assume q>0 & n>0; then
    q>0 & n>=1 by NAT_1:14; then
    A2: q = (n -Root q)|^n by PREPOWER:19;
    n -Root q in REAL by XREAL_0:def 1;
    hence thesis by A2;
  end;
