
theorem Th1284:
Sum digits(3775,10) = 22
proof
  thus Sum digits(3775,10) = Sum <%5,7,7%>+Sum <%3%> by Th1283,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%7%> + Sum <%3%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%7%> + Sum <%3%> by AFINSQ_2:54
  .= (5 + 7 + 7) + Sum <%3%> by AFINSQ_2:53
  .= 19 + 3 by AFINSQ_2:53
  .= 22;
end;
