Binders library that's used in many Iris developments.

See merge request iris/stdpp!67

This closes issue #25.

Improve performance of `set_solver`

Closes #29 and iris#232

See merge request iris/stdpp!66

gmultiset lemmas

See merge request !65

Add `map_delete_zip_with`

See merge request !64

More efficient list encoding for Countable

See merge request iris/stdpp!62

This changes the encoding used for finite lists of values of countable
types to be linear instead of exponential. The encoding works by
duplicating bits of each element so that 0 -> 00 and 1 -> 11, and then
separating each element with 10. The top 1-bits are not kept since we
know a 10 is starting a new element which ends with a 1.

Fix #28

Hopefully this fixes iris#232

move the (very brief) contribution guide to the README

See merge request !60

Make `gset` a `Definition` instead of `Notation`.

See merge request !59

This fixes an issue in orc11.

Overhaul of the `Infinite`/`Fresh` infrastructure

See merge request !58

- The class `Infinite A` is now defined as having a function
  `fresh : list A → A`, that given a list `xs`, gives an element `x ∉ xs`.
- For most types this `fresh` function has a sensible computable behavior,
  for example:
  + For numbers, it yields one added to the maximal element in `xs`.
  + For strings, it yields the first string representation of a number that is
    not in `xs`.
- For any type `C` of finite sets with elements of infinite type `A`, we lift
  the fresh function to `C → A`.

As a consequence:

- It is now possible to pick fresh elements from _any_ finite set and from
  _any_ list with elements of an infinite type. Before it was only possible
  for specific finite sets, e.g. `gset`, `pset`, ...
- It makes the code more uniform. There was a lot of overlap between having a
  `Fresh` and an `Infinite` instance. This got unified.