
theorem Th701:
Sum digits(3720,10) = 12
proof
  thus Sum digits(3720,10) = Sum <%0,2,7%>+Sum <%3%> by Th700,AFINSQ_2:55
  .= Sum <%0,2%> + Sum <%7%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 2) + Sum <%7%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 2 + 7) + Sum <%3%> by AFINSQ_2:53
  .= 9 + 3 by AFINSQ_2:53
  .= 12;
end;
