Generator tables - multiplication tables defined only for multiplying by
generators.

Independent sets of semigroups represented by multiplication tables.

Functions for dealing with abstract multiplication tables of semigroups.
The multiplicative elements are represented by their indices in a
given sequence. The tables are vectors of vectors (the rows of the table),
so multiplication is just a constant-time look up.
Functionality for multiplying subsets of elements and computing closures
and thus enumerating subsemigroups. The subsemigroups can be stored in
efficient int-sets.

Constructing morphisms and morphic relations for multiplication tables.
input: two multiplication tables (source, target)
output: hash-maps describing morphisms, index i -> image

These functions are relatively inefficient (compared to generator table
methods).
They are for reference purposes, not for the high-end computations.

This is a reference implementation for the paper:
Finite Computational Structures and Implementations: Semigroups and
Morphic Relations
International Journal of Networking and Computing,
Volume 7, Number 2, pages 318-335, July 2017
https://doi.org/10.15803/ijnc.7.2_318