
theorem Th823:
Sum digits(1232,10) = 8
proof
  thus Sum digits(1232,10) = Sum <%2,3,2%>+Sum <%1%> by Th822,AFINSQ_2:55
  .= Sum <%2,3%> + Sum <%2%> + Sum <%1%> by AFINSQ_2:55
  .= (2 + 3) + Sum <%2%> + Sum <%1%> by AFINSQ_2:54
  .= (2 + 3 + 2) + Sum <%1%> by AFINSQ_2:53
  .= 7 + 1 by AFINSQ_2:53
  .= 8;
end;
