
theorem Th1154:
Sum digits(1575,10) = 18
proof
  thus Sum digits(1575,10) = Sum <%5,7,5%>+Sum <%1%> by Th1153,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%5%> + Sum <%1%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%5%> + Sum <%1%> by AFINSQ_2:54
  .= (5 + 7 + 5) + Sum <%1%> by AFINSQ_2:53
  .= 17 + 1 by AFINSQ_2:53
  .= 18;
end;
