
theorem Th1178:
Sum digits(2025,10) = 9
proof
  thus Sum digits(2025,10) = Sum <%5,2,0%>+Sum <%2%> by Th1177,AFINSQ_2:55
  .= Sum <%5,2%> + Sum <%0%> + Sum <%2%> by AFINSQ_2:55
  .= (5 + 2) + Sum <%0%> + Sum <%2%> by AFINSQ_2:54
  .= (5 + 2 + 0) + Sum <%2%> by AFINSQ_2:53
  .= 7 + 2 by AFINSQ_2:53
  .= 9;
end;
