reserve X for BCI-algebra;
reserve I for Ideal of X;
reserve a,x,y,z,u for Element of X;
reserve f,f9,g for sequence of  the carrier of X;
reserve j,i,k,n,m for Nat;

theorem Th2:
  (x,y) to_power 1 = x\y
proof
  consider f such that
A1: (x,y) to_power 1 = f.1 and
A2: f.0 = x & for j st j < 1 holds f.(j + 1) = f.j \ y by Def1;
  f.(0+1) = x\y by A2,NAT_1:3;
  hence thesis by A1;
end;
