
theorem Th1206:
Sum digits(2475,10) = 18
proof
  thus Sum digits(2475,10) = Sum <%5,7,4%>+Sum <%2%> by Th1205,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%4%> + Sum <%2%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%4%> + Sum <%2%> by AFINSQ_2:54
  .= (5 + 7 + 4) + Sum <%2%> by AFINSQ_2:53
  .= 16 + 2 by AFINSQ_2:53
  .= 18;
end;
