
theorem Th358:
Sum digits(874,10) = 19
proof
  thus Sum digits(874,10) = Sum <%4,7%>+Sum <%8%> by Th357,AFINSQ_2:55
  .= (4 + 7) + Sum <%8%> by AFINSQ_2:54
  .= 11 + 8 by AFINSQ_2:53
  .= 19;
end;
