WeylFilling -- a Young tableau stored row-wise for the Weyl-module basis

A WeylFilling is a Young tableau of partition shape $\lambda$, stored as the list of its rows. A filling is represented by new WeylFilling from {r_1, r_2, ..., r_k}, where r_i is the list of entries in the $i$-th row (top-to-bottom, left-to-right within each row), of length $\lambda_i$.

The row-wise storage matches the ambient decomposition of the Weyl module $$W_\lambda(E) \;\subseteq\; \textstyle\bigotimes_{i=1}^{r} D^{\lambda_i}(E),$$ so each row directly corresponds to one divided-power tensor factor. Entries in a row are stored in sorted (weakly-increasing) order since divided powers of a free module have a basis indexed by multisets; see dividedPower.

The constructor weyl with a single List argument wraps a list of rows into a WeylFilling; the two-argument form weyl(lambda, f) builds the induced module map, see weyl(List,Matrix).

A WeylFilling is Weyl-semistandard (= Weyl-standard in the terminology of this package) if its rows are weakly increasing and its columns are strictly increasing. Over $\mathbb{Z}$ the Weyl-standard fillings of shape $\lambda$ with entries in $\{0,\ldots,d-1\}$ index a free basis of $W_\lambda(R^d)$.

Comparison ?, equality ==, and row access T_i / T_{i_0, i_1, ...} are all defined and mirror the corresponding operations on Filling (with rows in the role of columns).