
theorem Th837:
Sum digits(1408,10) = 13
proof
  thus Sum digits(1408,10) = Sum <%8,0,4%>+Sum <%1%> by Th836,AFINSQ_2:55
  .= Sum <%8,0%> + Sum <%4%> + Sum <%1%> by AFINSQ_2:55
  .= (8 + 0) + Sum <%4%> + Sum <%1%> by AFINSQ_2:54
  .= (8 + 0 + 4) + Sum <%1%> by AFINSQ_2:53
  .= 12 + 1 by AFINSQ_2:53
  .= 13;
end;
