A (left) semigroup/monoid/group action of G on P is simply the implementation of a method actl(g, p), or g |+|> p, such that:
1. `(g |+| h) |+|> p === g |+|> (h |+|> p)` for all `g`, `h` in `G` and `p` in `P`.
2. `id |+|> p === p` for all `p` in `P` (if `id` is defined)
- Companion
- object