Discrete helpers/sig perm

This is an extension of the class Perm with added negators. Signed permutations of length $$n$$ are the $$2^n \cdot n!$$ elements of the of dimension $$n$$. (See e.g. the full octahedral group for the 48 permutations of the cube.)

This class has been created to model transformations between Boolean functions in the same clan. (See Studies of Euler diagrams/transformations.)

The pattern of negations can be described in two different ways: When a signed permutation is denoted by a pair (m, n), it is usually the valneg index m and the permutation index n. But there are cases, where the keyneg index is the better choice. (See here and here.) The keyneg index is often shown in a square. E.g. the signed permutation (~3, 1, ~2, 0) has keyneg index, valneg index and permutation index.
 * valneg: which values are negated (or which rows of the permutations matrix)
 * keyneg: which places are negated (or which columns of the permutations matrix)

This is a subclass of, making the instances comparable.

Schoute permutation
The property  is inherited from. (See there.) These are signed Schoute permutations.

parity
Like for normal permutations, the corresponds to the determinant of the matrix. (But the metribute inherited from Perm is wrong.)