refactor(library/data/sigma): break file into smaller pieces to reduce dependencies

library/data/sigma/decl.lean

@@ -0,0 +1,9 @@
+-- Copyright (c) 2014 Microsoft Corporation. All rights reserved.
+-- Released under Apache 2.0 license as described in the file LICENSE.
+-- Author: Leonardo de Moura, Jeremy Avigad, Floris van Doorn
+import logic.eq logic.heq data.unit
+
+structure sigma {A : Type} (B : A → Type) :=
+dpair :: (dpr1 : A) (dpr2 : B dpr1)
+
+notation `Σ` binders `,` r:(scoped P, sigma P) := r

library/data/sigma/default.lean

@@ -0,0 +1,4 @@
+-- Copyright (c) 2014 Microsoft Corporation. All rights reserved.
+-- Released under Apache 2.0 license as described in the file LICENSE.
+-- Author: Leonardo de Moura, Jeremy Avigad, Floris van Doorn
+import data.sigma.decl data.sigma.thms

library/data/sigma/thms.lean

@@ -1,14 +1,9 @@
 -- Copyright (c) 2014 Microsoft Corporation. All rights reserved.
 -- Released under Apache 2.0 license as described in the file LICENSE.
 -- Author: Leonardo de Moura, Jeremy Avigad, Floris van Doorn
-import logic.inhabited logic.cast
+import data.sigma.decl
 open inhabited eq.ops
 
-structure sigma {A : Type} (B : A → Type) :=
-dpair :: (dpr1 : A) (dpr2 : B dpr1)
-
-notation `Σ` binders `,` r:(scoped P, sigma P) := r
-
 namespace sigma
   universe variables u v
   variables {A A' : Type.{u}} {B : A → Type.{v}} {B' : A' → Type.{v}}