
theorem Th1012:
Sum digits(1242,10) = 9
proof
  thus Sum digits(1242,10) = Sum <%2,4,2%>+Sum <%1%> by Th1011,AFINSQ_2:55
  .= Sum <%2,4%> + Sum <%2%> + Sum <%1%> by AFINSQ_2:55
  .= (2 + 4) + Sum <%2%> + Sum <%1%> by AFINSQ_2:54
  .= (2 + 4 + 2) + Sum <%1%> by AFINSQ_2:53
  .= 8 + 1 by AFINSQ_2:53
  .= 9;
end;
