
theorem Th1164:
Sum digits(1775,10) = 20
proof
  thus Sum digits(1775,10) = Sum <%5,7,7%>+Sum <%1%> by Th1163,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%7%> + Sum <%1%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%7%> + Sum <%1%> by AFINSQ_2:54
  .= (5 + 7 + 7) + Sum <%1%> by AFINSQ_2:53
  .= 19 + 1 by AFINSQ_2:53
  .= 20;
end;
