
theorem Th1292:
Sum digits(3925,10) = 19
proof
  thus Sum digits(3925,10) = Sum <%5,2,9%>+Sum <%3%> by Th1291,AFINSQ_2:55
  .= Sum <%5,2%> + Sum <%9%> + Sum <%3%> by AFINSQ_2:55
  .= (5 + 2) + Sum <%9%> + Sum <%3%> by AFINSQ_2:54
  .= (5 + 2 + 9) + Sum <%3%> by AFINSQ_2:53
  .= 16 + 3 by AFINSQ_2:53
  .= 19;
end;
