diff --git a/doc/ast.txt b/doc/ast.txt
new file mode 100755
index 0000000..72958b3
--- /dev/null
+++ b/doc/ast.txt
@@ -0,0 +1,55 @@
+##############################################################################
+                               ABSTRACT SYNTAX
+##############################################################################
+
+P = Program { D } E
+
+D = ClassDef name [ name ] { M }
+# where [ name ] corresponds to [ "extends" ident ] in the concrete syntax
+
+M = FieldDecl name T
+  | MethodDef name { name T } T E
+# where { name T } corresponds to [ Formal { "," Formal } ] in the con. syntax
+
+T = ClassType name
+  | IntType
+  | NullType
+
+S = While E { S }
+  | Var name T E
+  | Set name E
+  | Do E
+  | PrintInt E
+  | PrintChar E
+
+E = Ident name
+  | New name { E }
+  | Select E name
+  | Call E name { E }
+  | IntLit int
+  | NullLit
+  | Unop U E
+  | Binop B E E
+  | ReadInt
+  | ReadChar
+  | If E E E
+  | Block { S } E
+
+U = Not
+  | Neg
+
+B = Add
+  | Sub
+  | Mul
+  | Div
+  | Mod
+  | Eq
+  | Ne
+  | Lt
+  | Le
+  | Gt
+  | Ge
+  | And
+
+##############################################################################
+$Id$