
theorem Th1010:
Sum digits(1219,10) = 13
proof
  thus Sum digits(1219,10) = Sum <%9,1,2%>+Sum <%1%> by Th1009,AFINSQ_2:55
  .= Sum <%9,1%> + Sum <%2%> + Sum <%1%> by AFINSQ_2:55
  .= (9 + 1) + Sum <%2%> + Sum <%1%> by AFINSQ_2:54
  .= (9 + 1 + 2) + Sum <%1%> by AFINSQ_2:53
  .= 12 + 1 by AFINSQ_2:53
  .= 13;
end;
