
theorem Th1282:
Sum digits(3750,10) = 15
proof
  thus Sum digits(3750,10) = Sum <%0,5,7%>+Sum <%3%> by Th1281,AFINSQ_2:55
  .= Sum <%0,5%> + Sum <%7%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 5) + Sum <%7%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 5 + 7) + Sum <%3%> by AFINSQ_2:53
  .= 12 + 3 by AFINSQ_2:53
  .= 15;
end;
