diff --git a/src/opt/ufar/UfarPth.cpp b/src/opt/ufar/UfarPth.cpp
index 085614275..6df45657f 100755
--- a/src/opt/ufar/UfarPth.cpp
+++ b/src/opt/ufar/UfarPth.cpp
@@ -11,15 +11,15 @@
 #include "opt/untk/NtkNtk.h"
 #include "UfarPth.h"
 
-ABC_NAMESPACE_IMPL_START
-
-extern "C" {
+ABC_NAMESPACE_HEADER_START
     Abc_Ntk_t *   Abc_NtkFromAigPhase( Aig_Man_t * pAig );
     int           Abc_NtkDarBmc3( Abc_Ntk_t * pAbcNtk, Saig_ParBmc_t * pBmcPars, int fOrDecomp );
     Wla_Man_t * Wla_ManStart( Wlc_Ntk_t * pNtk, Wlc_Par_t * pPars );
     void Wla_ManStop( Wla_Man_t * pWla );
     int Wla_ManSolve( Wla_Man_t * pWla, Wlc_Par_t * pPars );
-}
+ABC_NAMESPACE_HEADER_END
+
+ABC_NAMESPACE_IMPL_START
 
 static volatile int  g_nRunIds = 0;             // the number of the last prover instance
 int Ufar_CallBackToStop( int RunId ) { assert( RunId <= g_nRunIds ); return RunId < g_nRunIds; }
diff --git a/src/opt/untk/NtkNtk.cpp b/src/opt/untk/NtkNtk.cpp
index ada25c2b2..0ee5e5fd7 100755
--- a/src/opt/untk/NtkNtk.cpp
+++ b/src/opt/untk/NtkNtk.cpp
@@ -20,9 +20,7 @@
 #include "NtkNtk.h"
 #include "Netlist.h"
 
-ABC_NAMESPACE_IMPL_START
-
-extern "C" {
+ABC_NAMESPACE_HEADER_START
     Abc_Ntk_t * Abc_NtkFromAigPhase( Aig_Man_t * pMan );
     int Abc_NtkDarPdr( Abc_Ntk_t * pNtk, Pdr_Par_t * pPars );
     int Abc_NtkDarBmc3( Abc_Ntk_t * pNtk, Saig_ParBmc_t * pPars, int fOrDecomp );
@@ -36,7 +34,9 @@ extern "C" {
     int Wla_ManSolve( Wla_Man_t * pWla, Wlc_Par_t * pPars );
     Gia_Man_t * Wlc_NtkBitBlast2( Wlc_Ntk_t * p, Vec_Int_t * vBoxIds );
     //void Gia_ManPrintStats( Gia_Man_t * p, Gps_Par_t * pPars );
-}
+ABC_NAMESPACE_HEADER_END
+
+ABC_NAMESPACE_IMPL_START
 
 using namespace std;
 
diff --git a/src/opt/util/util.cpp b/src/opt/util/util.cpp
old mode 100755
new mode 100644
index f20588466..47101c36b
--- a/src/opt/util/util.cpp
+++ b/src/opt/util/util.cpp
@@ -12,6 +12,17 @@
 #include "misc/util/abc_namespaces.h"
 #include "util.h"
 
+#ifdef __linux__
+#include <sys/prctl.h>
+#elif defined(__APPLE__)
+#include <thread>
+#include <cassert>
+#include <cerrno>
+#include <sys/types.h>
+#include <sys/event.h>
+#include <sys/time.h>
+#endif
+
 ABC_NAMESPACE_IMPL_START
 
 using namespace std;
@@ -50,14 +61,8 @@ void OptMgr::PrintUsage() {
     }
 }
 
-ABC_NAMESPACE_IMPL_END
-
 #ifdef __linux__
 
-#include <sys/prctl.h>
-
-ABC_NAMESPACE_IMPL_START
-
 void kill_on_parent_death(int sig)
 {
     // kill process if parent dies
@@ -71,21 +76,8 @@ void kill_on_parent_death(int sig)
     }
 }
 
-ABC_NAMESPACE_IMPL_END
-
 #elif defined(__APPLE__)
 
-#include <thread>
-
-#include <cassert>
-#include <cerrno>
-
-#include <sys/types.h>
-#include <sys/event.h>
-#include <sys/time.h>
-
-ABC_NAMESPACE_IMPL_START
-
 template <typename Func>
 static auto retry_eintr(Func &&fn) -> decltype(fn())
 {
@@ -115,7 +107,7 @@ void kill_on_parent_death(int sig)
     kevent(kq, &change, 1, &event, 1, &ts);
 
     // however, if ppid died before the call to kevent, ppid might not be the pid of the parent
-    // in that case, the process it would be adopted by init, whose pid is 1
+    // in that case, it would be adopted by init, whose pid is 1
     if( getppid() == 1 )
     {
       raise(sig);
@@ -132,16 +124,12 @@ void kill_on_parent_death(int sig)
   monitor_thread.detach();
 }
 
-ABC_NAMESPACE_IMPL_END
-
 #else // neither linux or OS X
 
-ABC_NAMESPACE_IMPL_START
-
 void kill_on_parent_death(int sig)
 {
 }
 
-ABC_NAMESPACE_IMPL_END
-
 #endif
+
+ABC_NAMESPACE_IMPL_END