add a readme for the examples folder

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+Cubical Type Theory: examples
+=============================
+
+This folder contains a lot of examples implemented using
+cubicaltt. The files contain:
+
+binnat.ctt - Binary natural numbers and isomorphism to unary
+             numbers. Example of data and program refinement by doing
+             a proof for unary numbers by computation with binary
+             numbers.
+
+bool.ctt - Booleans. Proof that bool = bool by negation and various
+           other simple examples.
+
+category.ctt - Categories. Structure identity principle. Pullbacks.
+
+circle.ctt - The circle as a HIT. Computation of winding numbers.
+
+collection.ctt - This file proves that the collection of all
+                 sets is a groupoid.
+
+csystem.ctt - Definition of C-systems and universe
+              categories. Construction of a C-system from a universe
+              category.
+
+demo.ctt - Demo of the system.
+
+discor.ctt - or A B is discrete if A and B are.
+
+equiv.ctt - Definition of equivalences and various results on these,
+            including the "graduate lemma".
+
+groupoidTrunc.ctt - The groupoid truncation as a HIT.
+
+hedberg.ctt - Hedbergs lemma: a type with decidable equality is a set.
+
+helix.ctt - The loop space of the circle is equal to Z.
+
+hnat.ctt - Non-standard natural numbers as a HIT without any path
+           constructor.
+
+hz.ctt - Z defined as a (impredicative set) quotient of nat * nat
+ 
+idtypes.ctt - Identity types (variation of Path types with
+              definitional equality for J). Including a proof
+              univalence expressed only using Id.
+
+injective.ctt - Two definitions of injectivity and proof that they are
+                equal.
+
+int.ctt - The integers as nat + nat with proof that suc is an iso
+          giving a non-trivial path from Z to Z.
+
+integer.ctt - The integers as a HIT (identifying +0 with -0). Proof
+              that this representation is isomorphic to the one in
+              int.ctt
+
+interval.ctt - The interval as a HIT. Proof of function extensionality
+               from it.
+
+list.ctt - Lists. Various basic lemmas in "cubical style".
+
+nat.ctt - Natural numbers. Various basic lemmas in "cubical style".
+
+ordinal.ctt - Ordinals.
+
+pi.ctt - Characterization of equality in pi types.
+
+prelude.ctt - The prelude. Definition of Path types and basic
+              operations on them (refl, mapOnPath,
+              funExt...). Definition of prop, set and groupoid. Some
+              basic data types (empty, unit, or, and).
+
+propTrunc.ctt - Propositional truncation as a HIT. (WARNING: not
+                working correctly)
+
+retract.ctt - Definition of retract and section.
+
+setquot.ctt - Formalization of impredicative set quotients á la
+              Voevodsky.
+
+sigma.ctt - Various results about sigma types.
+
+subset.ctt - Two definitions of a subset and a proof that they are
+             equal.
+
+summary.ctt - Summary of where to find the results and examples from
+              the cubical type theory paper.
+
+susp.ctt - Suspension. Definition of the circle as the suspension of
+           bool and a proof that this is equal to the standard HIT
+           representation of the circle.
+
+torsor.ctt - Torsors. Proof that S1 is equal to BZ, the classifying
+             space of Z.
+
+torus.ctt - Proof that Torus = S1 * S1.
+
+univalence.ctt - Proofs of the univalence axiom.