
theorem Th1018:
Sum digits(1311,10) = 6
proof
  thus Sum digits(1311,10) = Sum <%1,1,3%>+Sum <%1%> by Th1017,AFINSQ_2:55
  .= Sum <%1,1%> + Sum <%3%> + Sum <%1%> by AFINSQ_2:55
  .= (1 + 1) + Sum <%3%> + Sum <%1%> by AFINSQ_2:54
  .= (1 + 1 + 3) + Sum <%1%> by AFINSQ_2:53
  .= 5 + 1 by AFINSQ_2:53
  .= 6;
end;
