Create tutorial.md

src/doc/tutorial.md

+Tutorial
+========
+
+Let us consider the problem of checking whether the following size function on a list is always greater or equal to 0.
+```scala
+def size[T](list: List[T]): BigInt = list match {
+  case Cons(x, xs) => 1 + size(xs)
+  case Nil() => 0
+}
+```
+
+Note that verifying this property requires the use of induction, something Inox does not deal with explicitly.
+However, Inox provides all the tools necessary to enable inductive reasonning, as we will see shortly.
+
+Let us start by setting up some useful imports:
+```scala
+import inox._
+import inox.trees._
+import inox.trees.dsl._
+```
+
+## ADT Definitions
+
+The dsl we just imported provides us with the following helper methods to define ADTs (see
+the [Definitions](/src/doc/API.md#definitions) section in the API documentation for more details):
+
+1. For ADT sort definitions
+```scala
+def mkSort(id: Identifier)
+          (tpNames: String*)
+          (cons: Seq[Identifier]): ADTSort
+```
+
+2. For ADT constructor definitions
+```scala
+def mkConstructor(id: Identifier)
+                 (tpNames: String*)
+                 (sort: Option[Identifier])
+                 (fieldBuilder: Seq[TypeParameter] => Seq[ValDef]): ADTConstructor
+```
+
+We therefore start by