
theorem Th159:
Sum digits(224,10) = 8
proof
  thus Sum digits(224,10) = Sum <%4,2%>+Sum <%2%> by Th158,AFINSQ_2:55
  .= (4 + 2) + Sum <%2%> by AFINSQ_2:54
  .= 6 + 2 by AFINSQ_2:53
  .= 8;
end;
