
theorem Th1312:
Sum digits(4175,10) = 17
proof
  thus Sum digits(4175,10) = Sum <%5,7,1%>+Sum <%4%> by Th1311,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%1%> + Sum <%4%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%1%> + Sum <%4%> by AFINSQ_2:54
  .= (5 + 7 + 1) + Sum <%4%> by AFINSQ_2:53
  .= 13 + 4 by AFINSQ_2:53
  .= 17;
end;
