
theorem Th707:
Sum digits(3780,10) = 18
proof
  thus Sum digits(3780,10) = Sum <%0,8,7%>+Sum <%3%> by Th706,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%7%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%7%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 8 + 7) + Sum <%3%> by AFINSQ_2:53
  .= 15 + 3 by AFINSQ_2:53
  .= 18;
end;
