/*
  swindyer : a little procedure to compute so-called
  Swinnerton-Dyer polynomials, which are interesting 
  because they are irreducible, but split into factors
  of degree at most 2 modulo every prime  

  input: plist --- list of primes 

*/
  
  
swindyer:=
proc(plist)
local result,i,l,fac,j;
begin
result:=1;
for i from 0 to 2^(nops(plist))-1 do
	l:=numlib::g_adic(i,2);
	fac:=hold(x);
	for j from 1 to nops(plist) do
		if op(l,j)=1 then 
			fac:=fac+sqrt(plist[j])
		else
			fac:=fac-sqrt(plist[j])
		end_if;
	end_for;
	result:=result*fac;
end_for;
result
end_proc: