diff --git a/src/deptree.cpp b/src/deptree.cpp
new file mode 100644
index 0000000..56ca8f4
--- /dev/null
+++ b/src/deptree.cpp
@@ -0,0 +1,145 @@
+#include "deptree.h"
+#include "globals.h"
+
+int DepTree::CreateNodeFromVar(const std::string& var, std::set<std::string>& used, std::set<DepTree*>& callstack)
+{
+ COUT(DEBUG)<<"DepTree::CreateNodeFromVar "<<var<<std::endl;
+ if(G_vars.count(var)==0)
+ {
+  COUT(ERROR)<<"Definition of variable "<<var<<" not found"<<std::endl;
+  return 1;
+ }
+
+ std::set<std::string> ids;
+
+ used.insert(var);
+ G_vars[var]->UsedIdents(ids);
+ type=DepTree::VAR;
+ name=var;
+
+ DepTree* d;
+ int ret;
+ callstack.insert(this);
+ for(auto& i:ids)
+ {
+  d=FindNodeByVar(i);
+  if(d==0)
+  {
+   auto n=*childrens.insert(new DepTree).first;
+   n->parents.insert(this);
+   ret=n->CreateNodeFromVar(i,used,callstack);
+   if(ret!=0)
+   {
+    COUT(ERROR)<<" in definition of variable "<<name<<std::endl;
+    return ret;
+   }
+  }
+  else
+  {
+   if(callstack.find(d)!=callstack.end())
+   {
+    COUT(ERROR)<<"Circular dependency of variable "<<name<<" from variable "<<i<<std::endl;
+    return 1;
+   }
+   childrens.insert(d);
+   d->parents.insert(this);
+  }
+ }
+ callstack.erase(this);
+
+ return 0;
+}
+
+
+int DepTree::CreateNodeFromSP(DepTree::NodeType list, std::vector<ObjectList*>::size_type ind, std::set<std::string>& used)
+{
+ if(list!=DepTree::SAVE && list!=DepTree::PRINT)
+ {
+  COUT(ERROR)<<"Internal error, incorrect NodeType in DepTree::CreateNodeFromSP()."<<std::endl;
+  return 2;
+ }
+ COUT(DEBUG)<<"DepTree::CreateNodeFromSP "<<((list==DepTree::SAVE)?G_tosave:G_toprint)[ind]->Dump()<<std::endl;
+
+ std::set<std::string> ids;
+ std::set<DepTree*> callstack;
+
+ type=list;
+ index=ind;
+
+ if(type==DepTree::SAVE) G_tosave[index]->UsedIdents(ids);
+ else if(type==DepTree::PRINT) G_toprint[index]->UsedIdents(ids);
+ DepTree* d;
+ int ret;
+ for(auto& i:ids)
+ {
+  d=FindNodeByVar(i);
+  if(d==0)
+  {
+   auto n=*childrens.insert(new DepTree).first;
+   n->parents.insert(this);
+   ret=n->CreateNodeFromVar(i,used,callstack);
+   if(ret!=0)
+   {
+    COUT(ERROR)<<" in "<<((type==DepTree::SAVE)?"save":"print")<<" directive "<<((type==DepTree::SAVE)?G_tosave:G_toprint)[index]->Dump()<<"."<<std::endl;
+    return ret;
+   }
+  }
+  else
+  {
+   childrens.insert(d);
+   d->parents.insert(this);
+  }
+ }
+
+ return 0;
+}
+
+
+int DepTree::CreateGlobalTree(std::set<std::string>& used)
+{
+ if(parents.size()!=0)
+ {
+  COUT(ERROR)<<"Internal error, DepTree::CreateGlobalTree() call for non-root node."<<std::endl;
+  return 2;
+ }
+
+ type=DepTree::ROOT;
+ for(int i=0; i<G_tosave.size(); i++)
+ {
+  auto n=*childrens.insert(new DepTree).first;
+  n->parents.insert(this);
+  auto ret=n->CreateNodeFromSP(DepTree::SAVE,i,used);
+  if(ret!=0) return ret;
+ }
+ for(int i=0; i<G_toprint.size(); i++)
+ {
+  auto n=*childrens.insert(new DepTree).first;
+  n->parents.insert(this);
+  auto ret=n->CreateNodeFromSP(DepTree::PRINT,i,used);
+  if(ret!=0) return ret;
+ }
+
+ return 0;
+}
+
+
+DepTree* DepTree::FindNodeByVarFromCurrent(const std::string& var) const
+{
+ if(type==DepTree::VAR && name==var) return const_cast<DepTree*>(this);
+
+ DepTree* d;
+ for(auto& i:childrens)
+ {
+  d=i->FindNodeByVarFromCurrent(var);
+  if(d!=0) return d;
+ }
+ return 0;
+}
+
+
+DepTree* DepTree::FindNodeByVar(const std::string& var) const
+{
+ const DepTree* curnode=this;
+ while(curnode->parents.size()!=0) curnode=*(curnode->parents.begin());
+ return curnode->FindNodeByVarFromCurrent(var);
+}
diff --git a/src/deptree.h b/src/deptree.h
new file mode 100644
index 0000000..99718f8
--- /dev/null
+++ b/src/deptree.h
@@ -0,0 +1,38 @@
+#ifndef DEPTREE_H
+#define DEPTREE_H
+#include <set>
+#include <vector>
+#include <string>
+#include "object.h"
+
+class DepTree
+{
+ enum NodeType {NOTDEF,ROOT,SAVE,PRINT,VAR};
+
+ std::set<DepTree*> parents;
+ std::set<DepTree*> childrens;
+ NodeType type;
+ std::vector<ObjectList*>::size_type index;
+ std::string name;
+
+ int CreateNodeFromVar(const std::string& var, std::set<std::string>& used, std::set<DepTree*>& callstack);
+ int CreateNodeFromSP(NodeType list, std::vector<ObjectList*>::size_type ind, std::set<std::string>& used);
+ DepTree* FindNodeByVarFromCurrent(const std::string& var) const;
+ DepTree* FindNodeByVar(const std::string& var) const;
+public:
+ DepTree():type(DepTree::NOTDEF) {}
+ DepTree(const DepTree&) = delete;
+ ~DepTree()
+ {
+  for(auto& i:parents) i->childrens.erase(this);
+  for(auto& i:childrens)
+  {
+   i->parents.erase(this);
+   if(i->parents.size()==0) delete i;
+  }
+ }
+
+ int CreateGlobalTree(std::set<std::string>& used);
+};
+
+#endif
diff --git a/src/globals.cpp b/src/globals.cpp
index 6962fbc..226861a 100644
--- a/src/globals.cpp
+++ b/src/globals.cpp
@@ -27,104 +27,3 @@ void RegisterFunction(const std::string& name, Func func)
 {
  G_funcs.emplace(name,func);
 }
-
-int DepTree::CreateNodeFromVar(const std::string& var, std::set<std::string>& used)
-{
- if(G_vars.count(var)==0)
- {
-  COUT(ERROR)<<"Definition of variable "<<var<<" not found."<<std::endl;
-  return 1;
- }
-
- std::vector<std::string> ids;
-
- used.insert(var);
- G_vars[var]->UsedIdents(ids);
- type=DepTree::VAR;
- name=var;
- nchild=ids.size();
- COUT(DEBUG)<<ids.size()<<std::endl;
- if(nchild!=0)
- {
-  childrens=new DepTree*[nchild];
-  for(unsigned int i=0;i<nchild;i++) {childrens[i]=new DepTree; childrens[i]->parent=this;}
-  for(unsigned int i=0;i<nchild;i++)
-  {
-   int ret;
-   ret=childrens[i]->CreateNodeFromVar(ids[i],used);
-   if(ret!=0)
-   {
-    COUT(ERROR)<<" in definition of variable "<<var<<"."<<std::endl;
-    return ret;
-   }
-  }
- }
- return 0;
-}
-
-
-int DepTree::CreateNodeFromSP(DepTree::NodeType list, std::vector<ObjectList*>::size_type ind, std::set<std::string>& used)
-{
- if(list!=DepTree::SAVE && list!=DepTree::PRINT)
- {
-  COUT(ERROR)<<"Internal error, incorrect NodeType in DepTree::CreateNodeFromSP()."<<std::endl;
-  return 2;
- }
-
- std::vector<std::string> ids;
-
- type=list;
- index=ind;
-
- if(type==DepTree::SAVE) G_tosave[index]->UsedIdents(ids);
- else if(type==DepTree::PRINT) G_toprint[index]->UsedIdents(ids);
- nchild=ids.size();
- if(nchild!=0)
- {
-  childrens=new DepTree*[nchild];
-  for(unsigned int i=0;i<nchild;i++) {childrens[i]=new DepTree; childrens[i]->parent=this;}
-  for(unsigned int i=0;i<nchild;i++)
-  {
-   int ret;
-   ret=childrens[i]->CreateNodeFromVar(ids[i],used);
-   if(ret!=0)
-   {
-    COUT(ERROR)<<" in print/save directive "<<G_toprint[index]->Dump()<<"."<<std::endl;
-    return ret;
-   }
-  }
- }
-
- return 0;
-}
-
-
-int DepTree::CreateGlobalTree(std::set<std::string>& used)
-{
- if(parent!=0)
- {
-  COUT(ERROR)<<"Internal error, DepTree::CreateGlobalTree() call for non-root node."<<std::endl;
-  return 2;
- }
-
- unsigned int i,j;
- int ret;
-
- type=DepTree::ROOT;
- nchild=G_toprint.size()+G_tosave.size();
- if(nchild!=0) childrens=new DepTree*[nchild];
- for(i=0;i<nchild;i++) {childrens[i]=new DepTree; childrens[i]->parent=this;}
- i=0;
- for(j=0;j<G_tosave.size();j++)
- {
-  ret=childrens[i++]->CreateNodeFromSP(DepTree::SAVE,j,used);
-  if(ret!=0) return ret;
- }
- for(j=0;j<G_toprint.size();j++)
- {
-  ret=childrens[i++]->CreateNodeFromSP(DepTree::PRINT,j,used);
-  if(ret!=0) return ret;
- }
-
- return 0;
-}
diff --git a/src/globals.h b/src/globals.h
index 395fd81..6bd37cd 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -24,28 +24,4 @@ extern "C" {
 EXPORT void RegisterFunction(const std::string& name, Func func);
 }
 
-class DepTree
-{
- enum NodeType {NOTDEF,ROOT,SAVE,PRINT,VAR};
-
- DepTree* parent;
- unsigned int nchild;
- DepTree** childrens;
- NodeType type;
- std::vector<ObjectList*>::size_type index;
- std::string name;
-
- int CreateNodeFromVar(const std::string& var, std::set<std::string>& used);
- int CreateNodeFromSP(NodeType list, std::vector<ObjectList*>::size_type ind, std::set<std::string>& used);
-public:
- DepTree():parent(0),nchild(0),childrens(0),type(DepTree::NOTDEF) {}
- DepTree(const DepTree&) = delete;
- ~DepTree()
- {
-  if(childrens!=0) for(unsigned int i=0; i<nchild; i++) delete childrens[i];
-  delete[] childrens;
- }
-
- int CreateGlobalTree(std::set<std::string>& used);
-};
 #endif
diff --git a/src/init.h b/src/init.h
index df124d2..4a1daf7 100644
--- a/src/init.h
+++ b/src/init.h
@@ -4,7 +4,7 @@
 #define YY_TYPEDEF_YY_SCANNER_T
 typedef void* yyscan_t;
 #endif
-#include "globals.h"
+#include "deptree.h"
 
 int ParseConfigFile(char* config);
 int RegisterArifmeticFunctions();
diff --git a/src/object.h b/src/object.h
index 270f746..6d09ecd 100644
--- a/src/object.h
+++ b/src/object.h
@@ -65,8 +65,8 @@ public:
   return true;
  }
  virtual std::string Dump() const {return "%"+Type()+"%";}
- virtual void UsedFuncs(std::vector<std::string>& funcs) const {}
- virtual void UsedIdents(std::vector<std::string>& ids) const {}
+ virtual void UsedFuncs(std::set<std::string>& funcs) const {}
+ virtual void UsedIdents(std::set<std::string>& ids) const {}
 };
 
 // Template for objects without specific constructor/destructor
@@ -151,8 +151,8 @@ public:
  const ObjectBase* Value() const {return val;}
  void SetPair(const std::string& n, ObjectBase* v) {if(!Exist()) {name=n; val=v;}}
  std::string Dump() const override { return Name()+"="+val->Dump(); }
- void UsedFuncs(std::vector<std::string>& funcs) const override {return val->UsedFuncs(funcs);}
- void UsedIdents(std::vector<std::string>& ids) const override {return val->UsedIdents(ids);}
+ void UsedFuncs(std::set<std::string>& funcs) const override {return val->UsedFuncs(funcs);}
+ void UsedIdents(std::set<std::string>& ids) const override {return val->UsedIdents(ids);}
 };
 
 // Class for objects list
@@ -189,8 +189,8 @@ public:
   if(vals.size()!=0) s.resize(s.length()-2);
   return s+")";
  }
- void UsedFuncs(std::vector<std::string>& funcs) const override {for(auto& i: vals) i->UsedFuncs(funcs);}
- void UsedIdents(std::vector<std::string>& ids) const override {for(auto& i: vals) i->UsedIdents(ids);}
+ void UsedFuncs(std::set<std::string>& funcs) const override {for(auto& i: vals) i->UsedFuncs(funcs);}
+ void UsedIdents(std::set<std::string>& ids) const override {for(auto& i: vals) i->UsedIdents(ids);}
 };
 
 // Class for storing identifiers
@@ -212,7 +212,7 @@ public:
  std::string Name() const {return name;}
  void SetName(std::string s) {ParseName(s);}
  std::string Dump() const override {return fullname;};
- void UsedIdents(std::vector<std::string>& ids) const override {ids.push_back(name);}
+ void UsedIdents(std::set<std::string>& ids) const override {ids.insert(name);}
 };
 
 // Class for storing functions
@@ -237,8 +237,8 @@ public:
  std::string Name() const {return name;}
  void SetName(std::string s) {name=s;}
  std::string Dump() const override {return Name()+args->Dump();};
- void UsedFuncs(std::vector<std::string>& funcs) const override {funcs.push_back(name); args->UsedFuncs(funcs);}
- void UsedIdents(std::vector<std::string>& ids) const override {args->UsedIdents(ids);}
+ void UsedFuncs(std::set<std::string>& funcs) const override {funcs.insert(name); args->UsedFuncs(funcs);}
+ void UsedIdents(std::set<std::string>& ids) const override {args->UsedIdents(ids);}
 };
 
 #endif