
theorem Th1006:
Sum digits(1173,10) = 12
proof
  thus Sum digits(1173,10) = Sum <%3,7,1%>+Sum <%1%> by Th1005,AFINSQ_2:55
  .= Sum <%3,7%> + Sum <%1%> + Sum <%1%> by AFINSQ_2:55
  .= (3 + 7) + Sum <%1%> + Sum <%1%> by AFINSQ_2:54
  .= (3 + 7 + 1) + Sum <%1%> by AFINSQ_2:53
  .= 11 + 1 by AFINSQ_2:53
  .= 12;
end;
