diff --git a/src/attackminimize.c b/src/attackminimize.c
index 869a124..13ef899 100644
--- a/src/attackminimize.c
+++ b/src/attackminimize.c
@@ -14,7 +14,7 @@ int cTod = 0;
  *@param tb The attack buffer.
  *@param ev The reference event index.
  */
-void markback(System sys, struct tracebuf *tb, int ev)
+void markback(const System sys, struct tracebuf *tb, int ev)
 {
 	int run = tb->run[ev];
 
@@ -53,7 +53,7 @@ void markback(System sys, struct tracebuf *tb, int ev)
 }
 
 //! Minimize the attack.
-void attackMinimize(System sys, struct tracebuf *tb)
+void attackMinimize(const System sys, struct tracebuf *tb)
 {
 	int i;
 	int j;
diff --git a/src/attackminimize.h b/src/attackminimize.h
index 5d0e8f8..efca999 100644
--- a/src/attackminimize.h
+++ b/src/attackminimize.h
@@ -1 +1 @@
-void attackMinimize(System sys, struct tracebuf *tb);
+void attackMinimize(const System sys, struct tracebuf *tb);
diff --git a/src/compiler.c b/src/compiler.c
index 734a108..95ebee0 100644
--- a/src/compiler.c
+++ b/src/compiler.c
@@ -74,7 +74,7 @@ static Role thisRole;
  *\sa oki_nisynch
  */
 void
-compile (System mysys, Tac tc, int maxrunsset)
+compile (const System mysys, Tac tc, int maxrunsset)
 {
   int i;
 
diff --git a/src/compiler.h b/src/compiler.h
index c6e19ca..b2668aa 100644
--- a/src/compiler.h
+++ b/src/compiler.h
@@ -1,7 +1,7 @@
 #ifndef COMPILER
 #define COMPILER
 
-void compile (System sys, Tac tc, int maxruns);
+void compile (const System sys, Tac tc, int maxruns);
 void preprocess (const System sys);
 
 #endif
diff --git a/src/debug.h b/src/debug.h
index c0f5278..2e3253d 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -1,8 +1,6 @@
 #ifndef DEBUG_H
 #define DEBUG_H
 
-#include "config.h"
-
 void debugSet (int level);
 int debugCond (int level);
 void debug (int level, char *string);
diff --git a/src/latex.c b/src/latex.c
index 74c63e5..9e46dcc 100644
--- a/src/latex.c
+++ b/src/latex.c
@@ -663,7 +663,7 @@ knowledgePrintLatex (Knowledge know)
 //! Display the attack in the systems attack buffer using LaTeX.
 
 void
-attackDisplayLatex (System sys)
+attackDisplayLatex (const System sys)
 {
   int i;
   struct tracebuf *tb;
diff --git a/src/latex.h b/src/latex.h
index e447395..f9730f0 100644
--- a/src/latex.h
+++ b/src/latex.h
@@ -13,8 +13,8 @@ void latexTimers(const System sys);
 void latexMSCStart();
 void latexMSCEnd();
 void latexLearnComment(const System sys, Termlist tl);
-void latexTracePrint(System sys);
-void attackDisplayLatex(System sys);
+void latexTracePrint(const System sys);
+void attackDisplayLatex(const System sys);
 void latexTermPrint (Term term, Termlist hl);
 void latexTermTuplePrint (Term term, Termlist hl);
 
diff --git a/src/output.c b/src/output.c
index f5c3206..3764343 100644
--- a/src/output.c
+++ b/src/output.c
@@ -25,7 +25,7 @@ linePrint (int i)
 }
 
 int
-correspondingSend (System sys, int rd)
+correspondingSend (const System sys, int rd)
 {
 
   int labelMatch = 0;
@@ -198,7 +198,7 @@ correspondingSend (System sys, int rd)
 }
 
 void
-tracePrint (System sys)
+tracePrint (const System sys)
 {
   int i, j;
   int lastrid;
@@ -347,7 +347,7 @@ tracePrint (System sys)
 
 
 void
-attackDisplayAscii (System sys)
+attackDisplayAscii (const System sys)
 {
   int i, j;
   int length;
@@ -479,7 +479,7 @@ attackDisplayAscii (System sys)
 
 
 void
-attackDisplay (System sys)
+attackDisplay (const System sys)
 {
   if (!sys->report || sys->switchStatespace)
       return;
diff --git a/src/report.c b/src/report.c
index 0ca4a83..c169736 100644
--- a/src/report.c
+++ b/src/report.c
@@ -9,7 +9,7 @@ extern int globalLatex;
 
 /* reportQuit is called after each violation, because it might need to abort the process */
 void
-reportQuit (System sys)
+reportQuit (const System sys)
 {
   /* determine quit or not */
   if (sys->prune >= 3)
@@ -22,7 +22,7 @@ reportQuit (System sys)
 }
 
 void
-reportStart (System sys)
+reportStart (const System sys)
 {
   if (!sys->latex)
     {
@@ -34,7 +34,7 @@ reportStart (System sys)
 }
 
 void
-reportMid (System sys)
+reportMid (const System sys)
 {
   indent ();
   printf ("Trace length %i.\n", 1 + sys->step);
@@ -45,7 +45,7 @@ reportMid (System sys)
 
 
 void
-reportEnd (System sys)
+reportEnd (const System sys)
 {
   if (!sys->latex)
     {
@@ -56,7 +56,7 @@ reportEnd (System sys)
 }
 
 void
-reportSecrecy (System sys, Term t)
+reportSecrecy (const System sys, Term t)
 {
   if (!sys->report)
     {
diff --git a/src/report.h b/src/report.h
index 27b0e8d..232ce4c 100644
--- a/src/report.h
+++ b/src/report.h
@@ -1,6 +1,6 @@
 #ifndef REPORT
 #define REPORT
 
-void reportSecrecy (System sys, Term t);
+void reportSecrecy (const System sys, Term t);
 
 #endif
diff --git a/src/runs.c b/src/runs.c
index 74989d5..e29192d 100644
--- a/src/runs.c
+++ b/src/runs.c
@@ -150,7 +150,7 @@ systemReset (const System sys)
  *\sa systemDestroy()
  */
 void
-systemDone (System sys)
+systemDone (const System sys)
 {
   int run;
   int s;
@@ -176,7 +176,7 @@ systemDone (System sys)
 
 //! Approximate the number of states traversed using a double type.
 double
-statesApproximation (System sys)
+statesApproximation (const System sys)
 {
   if (sys->statesHigh == 0)
     return (double) sys->statesLow;
@@ -186,14 +186,14 @@ statesApproximation (System sys)
 
 //! Print a short version of the number of states.
 void
-statesPrintShort (System sys)
+statesPrintShort (const System sys)
 {
   fprintf (stderr,"%.3e", statesApproximation (sys));
 }
 
 //! Print the number of states.
 void
-statesPrint (System sys)
+statesPrint (const System sys)
 {
   if (sys->statesHigh == 0)
     {
@@ -217,7 +217,7 @@ statesPrint (System sys)
  *\sa systemDone()
  */
 void
-systemDestroy (System sys)
+systemDestroy (const System sys)
 {
   memFree (sys->runs, sys->maxruns * sizeof (struct run));
   memFree (sys, sizeof (struct system));
@@ -230,7 +230,7 @@ systemDestroy (System sys)
  */
 
 void
-ensureValidRun (System sys, int run)
+ensureValidRun (const System sys, int run)
 {
   int i, oldsize;
 
@@ -336,7 +336,7 @@ runPrint (Roledef rd)
 
 //! Print all runs in the system structure.
 void
-runsPrint (System sys)
+runsPrint (const System sys)
 {
   int i;
 
@@ -750,7 +750,7 @@ roledefAdd (Roledef rd, int type, Term label, Term from, Term to, Term msg, Clai
  */
 
 void
-systemStart (System sys)
+systemStart (const System sys)
 {
   int i, s;
   Roledef rd;
@@ -953,7 +953,7 @@ rolesPrint (Role r)
  *@return True iff any agent in the list is untrusted.
  */
 int
-untrustedAgent (System sys, Termlist agents)
+untrustedAgent (const System sys, Termlist agents)
 {
   while (agents != NULL)
     {
diff --git a/src/runs.h b/src/runs.h
index fe5a22c..9c18c0e 100644
--- a/src/runs.h
+++ b/src/runs.h
@@ -268,15 +268,15 @@ typedef struct system *System;
 
 System systemInit ();
 void systemReset (const System sys);
-System systemDuplicate (System fromsys);
-void statesPrint (System sys);
-void statesPrintShort (System sys);
-void systemDestroy (System sys);
-void systemDone (System sys);
-void ensureValidRun (System sys, int run);
+System systemDuplicate (const System fromsys);
+void statesPrint (const System sys);
+void statesPrintShort (const System sys);
+void systemDestroy (const System sys);
+void systemDone (const System sys);
+void ensureValidRun (const System sys, int run);
 void roledefPrint (Roledef rd);
 void runPrint (Roledef rd);
-void runsPrint (System sys);
+void runsPrint (const System sys);
 Term agentOfRunRole (const System sys, const int run, const Term role);
 Term agentOfRun (const System sys, const int run);
 Roledef roledefDuplicate1 (const Roledef rd);
@@ -287,7 +287,7 @@ void roleInstance (const System sys, const Protocol protocol, const Role role,
 		   const Termlist tolist);
 Roledef roledefInit (int type, Term label, Term from, Term to, Term msg, Claimlist cl);
 Roledef roledefAdd (Roledef rd, int type, Term label, Term from, Term to, Term msg, Claimlist cl);
-void systemStart (System sys);
+void systemStart (const System sys);
 void indentActivate ();
 void indentSet (int i);
 void indent ();
@@ -299,7 +299,7 @@ void protocolPrint (Protocol p);
 void protocolsPrint (Protocol p);
 void rolePrint (Role r);
 void rolesPrint (Role r);
-int untrustedAgent (System sys, Termlist agents);
+int untrustedAgent (const System sys, Termlist agents);
 int getMaxTraceLength (const System sys);
 void agentsOfRunPrint (const System sys, const int run);
 void violatedClaimPrint (const System sys, int i);
diff --git a/src/terms.c b/src/terms.c
index aeca1eb..b21fc92 100644
--- a/src/terms.c
+++ b/src/terms.c
@@ -137,7 +137,7 @@ makeTermType (const int type, const Symbol symb, const int runid)
  *@return A term that is either not a variable, or has a NULL substitution.
  *\sa deVar()
  */
-Term
+__inline__ Term
 deVarScan (Term t)
 {
   while (realTermVariable (t) && t->subst != NULL)
diff --git a/src/terms.h b/src/terms.h
index b571c3c..deb97e5 100644
--- a/src/terms.h
+++ b/src/terms.h
@@ -63,7 +63,7 @@ void termsDone (void);
 Term makeTermEncrypt (Term t1, Term t2);
 Term makeTermTuple (Term t1, Term t2);
 Term makeTermType (const int type, const Symbol symb, const int runid);
-Term deVarScan (Term t);
+__inline__ Term deVarScan (Term t);
 #define substVar(t)		((t != NULL && t->type == VARIABLE && t->subst != NULL) ? 1 : 0)
 #define deVar(t)		( substVar(t) ? deVarScan(t->subst) : t)
 #define realTermLeaf(t)		(t != NULL && t->type <= LEAF)
diff --git a/src/varbuf.c b/src/varbuf.c
index bff1660..7e064a7 100644
--- a/src/varbuf.c
+++ b/src/varbuf.c
@@ -13,7 +13,7 @@
  */
 
 Varbuf
-varbufInit (System sys)
+varbufInit (const System sys)
 {
   Varbuf vb;
   Termlist tl;
@@ -55,7 +55,7 @@ varbufInit (System sys)
  */
 
 void
-varbufSet (System sys, Varbuf vb)
+varbufSet (const System sys, Varbuf vb)
 {
   Termlist tl1, tl2;
 
diff --git a/src/varbuf.h b/src/varbuf.h
index b68c348..6bc454d 100644
--- a/src/varbuf.h
+++ b/src/varbuf.h
@@ -3,8 +3,8 @@
 
 #include "runs.h"
 
-Varbuf varbufInit (System sys);
-void varbufSet (System sys, Varbuf vb);
+Varbuf varbufInit (const System sys);
+void varbufSet (const System sys, Varbuf vb);
 void varbufDone (Varbuf vb);
 
 #endif