diff --git a/ImportGraph/Cli.lean b/ImportGraph/Cli.lean
index 6f39cad..d6862f0 100644
--- a/ImportGraph/Cli.lean
+++ b/ImportGraph/Cli.lean
@@ -77,12 +77,12 @@ def importGraphCLI (args : Cli.Parsed) : IO UInt32 := do
 
   let outFiles ← try unsafe withImportModules #[{module := to}] {} (trustLevel := 1024) fun env => do
     let p := ImportGraph.getModule to
-    let ctx := { options := {}, fileName := "<input>", fileMap := default }
-    let state := { env }
     let mut graph := env.importGraph
     let unused ←
       match args.flag? "to"  with
       | some _ =>
+        let ctx := { options := {}, fileName := "<input>", fileMap := default }
+        let state := { env }
         let used ← Prod.fst <$> (CoreM.toIO (env.transitivelyRequiredModules to) ctx state)
         pure <| graph.fold (fun acc n _ => if used.contains n then acc else acc.insert n) NameSet.empty
       | none => pure NameSet.empty
@@ -121,8 +121,8 @@ def importGraphCLI (args : Cli.Parsed) : IO UInt32 := do
       let graph₂ := match args.flag? "to" with
         | none => graph.filter (fun n _ => n != to)
         | some _ => graph
-      let (out, _) ← CoreM.toIO (Graph.toGexf graph₂ p) ctx state
-      outFiles := outFiles.insert "gexf" out
+      let gexFile := Graph.toGexf graph₂ p env
+      outFiles := outFiles.insert "gexf" gexFile
     return outFiles
 
   catch err =>
diff --git a/ImportGraph/Gexf.lean b/ImportGraph/Gexf.lean
index e85fb8f..c6240f2 100644
--- a/ImportGraph/Gexf.lean
+++ b/ImportGraph/Gexf.lean
@@ -14,26 +14,22 @@ namespace ImportGraph
 
 open Elab Meta in
 /-- Filter Lean internal declarations -/
-def isBlackListed {m} [Monad m] [MonadEnv m] (declName : Name) : m Bool := do
-  if declName == ``sorryAx then return true
-  if declName matches .str _ "inj" then return true
-  if declName matches .str _ "noConfusionType" then return true
-  let env ← getEnv
-  pure <| declName.isInternalDetail
-   || isAuxRecursor env declName
-   || isNoConfusion env declName
-  <||> isRec declName <||> isMatcher declName
+def isBlackListed (env : Environment) (declName : Name) : Bool :=
+  declName == ``sorryAx
+  || declName matches .str _ "inj"
+  || declName matches .str _ "noConfusionType"
+  || declName.isInternalDetail
+  || isAuxRecursor env declName
+  || isNoConfusion env declName
+  || isRecCore env declName
+  || isMatcherCore env declName
 
-/-- Get all declarations in the specified file. -/
-def getDeclsInFile (module : Name) : CoreM NameSet := do
-  let env ← getEnv
-  match env.moduleIdxForModule? module with
-    | none => return {}
-    | some modIdx =>
-      let decls := env.const2ModIdx
-      let declsIn ← decls.foldM (fun acc n idx => do
-        if idx == modIdx && (! (← isBlackListed n)) then return acc.insert n else return acc) ({} : NameSet)
-      return declsIn
+/-- Get number of non-blacklisted declarations per file. -/
+def getNumberOfDeclsPerFile (env: Environment) : NameMap Nat :=
+  env.const2ModIdx.fold (fun acc n idx =>
+    let mod := env.allImportedModuleNames.get! idx
+    if isBlackListed env n then acc else acc.insert mod ((acc.findD mod 0) + 1)
+    ) {}
 
 /-- Gexf template for a node in th graph. -/
 def Gexf.nodeTemplate (n module : Name) (size : Nat) := s!"<node id=\"{n}\" label=\"{n}\"><attvalues><attvalue for=\"0\" value=\"{size}\" /><attvalue for=\"1\" value=\"{module.isPrefixOf n}\" /></attvalues></node>\n          "
@@ -49,14 +45,11 @@ Metadata can be stored in forms of attributes, currently we record the following
 * `in_module` (Bool): whether the file belongs to the main module
   (used to strip the first part of the name when displaying).
 -/
-def Graph.toGexf (graph : NameMap (Array Name)) (module : Name) : CoreM String := do
-  let sizes : NameMap Nat ← graph.foldM (fun acc n _ => do
-    pure <| acc.insert n (← getDeclsInFile n).size ) {}
-    -- graph.fold (fun acc _ i => i.foldl (fun acc₂ j => acc₂.insert j ((acc₂.findD j 0) + 1)) acc) {}
-
+def Graph.toGexf (graph : NameMap (Array Name)) (module : Name) (env : Environment) : String :=
+  let sizes : NameMap Nat := getNumberOfDeclsPerFile env
   let nodes : String := graph.fold (fun acc n _ => acc ++ nodeTemplate n module (sizes.findD n 0)) ""
   let edges : String := graph.fold (fun acc n i => acc ++ (i.foldl (fun b j => b ++ edgeTemplate j n) "")) ""
-  return s!"<?xml version='1.0' encoding='utf-8'?>
+  s!"<?xml version='1.0' encoding='utf-8'?>
     <gexf xmlns=\"http://www.gexf.net/1.2draft\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xsi:schemaLocation=\"http://www.gexf.net/1.2draft http://www.gexf.net/1.2draft/gexf.xsd\" version=\"1.2\">
       <meta>
         <creator>Lean ImportGraph</creator>