
theorem Th1266:
Sum digits(3475,10) = 19
proof
  thus Sum digits(3475,10) = Sum <%5,7,4%>+Sum <%3%> by Th1265,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%4%> + Sum <%3%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%4%> + Sum <%3%> by AFINSQ_2:54
  .= (5 + 7 + 4) + Sum <%3%> by AFINSQ_2:53
  .= 16 + 3 by AFINSQ_2:53
  .= 19;
end;
