
theorem Th1142:
Sum digits(1375,10) = 16
proof
  thus Sum digits(1375,10) = Sum <%5,7,3%>+Sum <%1%> by Th1141,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%3%> + Sum <%1%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%3%> + Sum <%1%> by AFINSQ_2:54
  .= (5 + 7 + 3) + Sum <%1%> by AFINSQ_2:53
  .= 15 + 1 by AFINSQ_2:53
  .= 16;
end;
