
theorem Th831:
Sum digits(1342,10) = 10
proof
  thus Sum digits(1342,10) = Sum <%2,4,3%>+Sum <%1%> by Th830,AFINSQ_2:55
  .= Sum <%2,4%> + Sum <%3%> + Sum <%1%> by AFINSQ_2:55
  .= (2 + 4) + Sum <%3%> + Sum <%1%> by AFINSQ_2:54
  .= (2 + 4 + 3) + Sum <%1%> by AFINSQ_2:53
  .= 9 + 1 by AFINSQ_2:53
  .= 10;
end;
