
theorem Th373:
Sum digits(420,10) = 6
proof
  thus Sum digits(420,10) = Sum <%0,2%>+Sum <%4%> by Th372,AFINSQ_2:55
  .= (0 + 2) + Sum <%4%> by AFINSQ_2:54
  .= 2 + 4 by AFINSQ_2:53
  .= 6;
end;
