
theorem Th1316:
Sum digits(4225,10) = 13
proof
  thus Sum digits(4225,10) = Sum <%5,2,2%>+Sum <%4%> by Th1315,AFINSQ_2:55
  .= Sum <%5,2%> + Sum <%2%> + Sum <%4%> by AFINSQ_2:55
  .= (5 + 2) + Sum <%2%> + Sum <%4%> by AFINSQ_2:54
  .= (5 + 2 + 2) + Sum <%4%> by AFINSQ_2:53
  .= 9 + 4 by AFINSQ_2:53
  .= 13;
end;
