reserve X for non empty set,
        x for Element of X,
        S for SigmaField of X,
        M for sigma_Measure of S,
        f,g,f1,g1 for PartFunc of X,REAL,
        l,m,n,n1,n2 for Nat,
        a,b,c for Real;
reserve k for positive Real;

theorem Th4:
a >= 0 & b > 0 implies a to_power b >= 0
proof
   assume A1: a >= 0;
   assume b > 0; then
   a = 0 implies a to_power b >= 0 by POWER:def 2;
   hence thesis by A1,POWER:34;
end;
