
theorem Th827:
Sum digits(1276,10) = 16
proof
  thus Sum digits(1276,10) = Sum <%6,7,2%>+Sum <%1%> by Th826,AFINSQ_2:55
  .= Sum <%6,7%> + Sum <%2%> + Sum <%1%> by AFINSQ_2:55
  .= (6 + 7) + Sum <%2%> + Sum <%1%> by AFINSQ_2:54
  .= (6 + 7 + 2) + Sum <%1%> by AFINSQ_2:53
  .= 15 + 1 by AFINSQ_2:53
  .= 16;
end;
