
theorem Th1044:
Sum digits(1656,10) = 18
proof
  thus Sum digits(1656,10) = Sum <%6,5,6%>+Sum <%1%> by Th1043,AFINSQ_2:55
  .= Sum <%6,5%> + Sum <%6%> + Sum <%1%> by AFINSQ_2:55
  .= (6 + 5) + Sum <%6%> + Sum <%1%> by AFINSQ_2:54
  .= (6 + 5 + 6) + Sum <%1%> by AFINSQ_2:53
  .= 17 + 1 by AFINSQ_2:53
  .= 18;
end;
