
theorem Th861:
Sum digits(1694,10) = 20
proof
  thus Sum digits(1694,10) = Sum <%4,9,6%>+Sum <%1%> by Th860,AFINSQ_2:55
  .= Sum <%4,9%> + Sum <%6%> + Sum <%1%> by AFINSQ_2:55
  .= (4 + 9) + Sum <%6%> + Sum <%1%> by AFINSQ_2:54
  .= (4 + 9 + 6) + Sum <%1%> by AFINSQ_2:53
  .= 19 + 1 by AFINSQ_2:53
  .= 20;
end;
