
theorem Th853:
Sum digits(1606,10) = 13
proof
  thus Sum digits(1606,10) = Sum <%6,0,6%>+Sum <%1%> by Th852,AFINSQ_2:55
  .= Sum <%6,0%> + Sum <%6%> + Sum <%1%> by AFINSQ_2:55
  .= (6 + 0) + Sum <%6%> + Sum <%1%> by AFINSQ_2:54
  .= (6 + 0 + 6) + Sum <%1%> by AFINSQ_2:53
  .= 12 + 1 by AFINSQ_2:53
  .= 13;
end;
