def dup_mirror(f, K):
 f = list(f)
 for i in range((len(f) - 2), (-1), (-2)):
  f[i] = (- f[i])
 return f

def dup_mirror ( f , K ) : f = list ( f ) for i in range ( ( len ( f ) - 2 ) , ( - 1 ) , ( - 2 ) ) : f [ i ] = ( - f [ i ] ) return f
evaluate efficiently the composition f in k[x] .