Signature of a permutation : signature

### 2.10.12 Signature of a permutation : `signature`

`signature` takes as argument a permutation.
`signature` returns the signature of the permutation given as argument.
The signature of a permutation is equal to :

- 1 if the permutation is equal to an even product of transpositions,
- -1 if the permutation is equal to an odd product of transpositions.

The signature of a cycle of size k is : (−1)k+1.
Input :

`signature([3,4,5,2,0,1])`

Output :

`-1`

Indeed `permu2cycles([3,4,5,2,0,1])=[[0,3,2,5,1,4]]`.