
theorem Th847:
Sum digits(1518,10) = 15
proof
  thus Sum digits(1518,10) = Sum <%8,1,5%>+Sum <%1%> by Th846,AFINSQ_2:55
  .= Sum <%8,1%> + Sum <%5%> + Sum <%1%> by AFINSQ_2:55
  .= (8 + 1) + Sum <%5%> + Sum <%1%> by AFINSQ_2:54
  .= (8 + 1 + 5) + Sum <%1%> by AFINSQ_2:53
  .= 14 + 1 by AFINSQ_2:53
  .= 15;
end;
