
theorem Th163:
Sum digits(252,10) = 9
proof
  thus Sum digits(252,10) = Sum <%2,5%>+Sum <%2%> by Th162,AFINSQ_2:55
  .= (2 + 5) + Sum <%2%> by AFINSQ_2:54
  .= 7 + 2 by AFINSQ_2:53
  .= 9;
end;
