
theorem Th793:
Sum digits(858,10) = 21
proof
  thus Sum digits(858,10) = Sum <%8,5%>+Sum <%8%> by Th792,AFINSQ_2:55
  .= (8 + 5) + Sum <%8%> by AFINSQ_2:54
  .= 13 + 8 by AFINSQ_2:53
  .= 21;
end;
