
theorem Th591:
Sum digits(2620,10) = 10
proof
  thus Sum digits(2620,10) = Sum <%0,2,6%>+Sum <%2%> by Th590,AFINSQ_2:55
  .= Sum <%0,2%> + Sum <%6%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 2) + Sum <%6%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 2 + 6) + Sum <%2%> by AFINSQ_2:53
  .= 8 + 2 by AFINSQ_2:53
  .= 10;
end;
