Straightening of a symmetric-group character indexed by a composition (source code)

= Straightening of a symmetric-group character indexed by a composition

For the alternating expression $\psi^\lambda$ indexed by an integer composition, swapping two adjacent entries of $\lambda-\mathrm{id}$ negates $\psi^\lambda$. If two entries coincide the expression vanishes; otherwise sorting produces, up to sign, the irreducible character indexed by the resulting partition.

= Character straightening
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