reserve A,B for Ordinal,
  K,M,N for Cardinal,
  x,x1,x2,y,y1,y2,z,u for object,X,Y,Z,X1,X2, Y1,Y2 for set,
  f,g for Function;

theorem
  exp(K,0) = 1
proof
  thus exp(K,0) = card {{}} by FUNCT_5:57
    .= 1 by CARD_1:30;
end;
