
theorem Th1176:
Sum digits(1975,10) = 22
proof
  thus Sum digits(1975,10) = Sum <%5,7,9%>+Sum <%1%> by Th1175,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%9%> + Sum <%1%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%9%> + Sum <%1%> by AFINSQ_2:54
  .= (5 + 7 + 9) + Sum <%1%> by AFINSQ_2:53
  .= 21 + 1 by AFINSQ_2:53
  .= 22;
end;
