Help1:=proc() : print(` W(n) `): end:

#W(n): inputs a pos. integer n, and outputs the set all sequences
#of length n in -1,1
W:=proc(n) local i,S,s:
option remember:

if n<0 then
  RETURN({}):
fi:

if n=0 then
 RETURN({[]}):
fi:

S:=W(n-1):

{ seq( [ op(s)  ,-1] , s in S), seq([op(s),1], s in S)} :



end: