diff --git a/source/dub/dependency.d b/source/dub/dependency.d
index b9948d7..ad63db7 100644
--- a/source/dub/dependency.d
+++ b/source/dub/dependency.d
@@ -1,381 +1,525 @@
-/**
-	Stuff with dependencies.
-
-	Copyright: © 2012 Matthias Dondorff
-	License: Subject to the terms of the MIT license, as written in the included LICENSE.txt file.
-	Authors: Matthias Dondorff, Sönke Ludwig
-*/
-module dub.dependency;
-
-import dub.utils;
-import dub.package_;
-
-import vibecompat.core.log;
-import vibecompat.core.file;
-import vibecompat.data.json;
-import vibecompat.inet.url;
-
-// todo: cleanup imports
-import std.array;
-import std.exception;
-import std.algorithm;
-import std.zip;
-import std.typecons;
-import std.conv;
-static import std.compiler;
-
-
-/**
-	A version in the format "major.update.bugfix".
-*/
-struct Version {
-	static const Version RELEASE = Version("0.0.0");
-	static const Version HEAD = Version(to!string(MAX_VERS)~"."~to!string(MAX_VERS)~"."~to!string(MAX_VERS));
-	static const Version INVALID = Version();
-	static const Version MASTER = Version(MASTER_STRING);
-	static const string MASTER_STRING = "~master";
-	
-	private { 
-		static const size_t MAX_VERS = 9999;
-		static const size_t MASTER_VERS = cast(size_t)(-1);
-		size_t[] v; 
-	}
-	
-	this(string vers)
-	{
-		enforce(vers == MASTER_STRING || count(vers, ".") == 2);
-		if(vers == MASTER_STRING) {
-			v = [MASTER_VERS, MASTER_VERS, MASTER_VERS];
-		} else {
-			auto toks = split(vers, ".");
-			v.length = toks.length;
-			foreach( i, t; toks ) v[i] = t.to!size_t();
-		}
-	}
-	
-	this(const Version o)
-	{
-		foreach(size_t vers; o.v)
-			v ~= vers;
-	}
-	
-	bool opEquals(ref const Version oth) const { return v == oth.v; }
-	bool opEquals(const Version oth) const { return v == oth.v; }
-	
-	int opCmp(ref const Version other)
-	const {
-		foreach( i; 0 .. min(v.length, other.v.length) )
-			if( v[i] != other.v[i] )
-				return cast(int)v[i] - cast(int)other.v[i];
-		return cast(int)v.length - cast(int)other.v.length;
-	}
-	int opCmp(in Version other) const { return opCmp(other); }
-	
-	string toString()
-	const {
-		enforce( v.length == 3 && (v[0] != MASTER_VERS || v[1] == v[2] && v[1] == MASTER_VERS) );
-		if(v[0] == MASTER_VERS) 
-			return MASTER_STRING;
-		string r;
-		for(size_t i=0; i<v.length; ++i) {
-			if(i!=0) r ~= ".";
-			r ~= to!string(v[i]);
-		}
-		return r;
-	}
-}
-
-/// Representing a dependency, which is basically a version string and a 
-/// compare methode, e.g. '>=1.0.0 <2.0.0' (i.e. a space separates the two
-/// version numbers)
-class Dependency {
-	private {
-		string m_cmpA;
-		Version m_versA;
-		string m_cmpB;
-		Version m_versB;
-	}
-
-	this( string ves ) {
-		enforce( ves.length > 0);
-		string orig = ves;
-		if(ves == Version.MASTER_STRING) {
-			m_cmpA = ">=";
-			m_cmpB = "<=";
-			m_versA = m_versB = Version(Version.MASTER);
-		}
-		else {
-			m_cmpA = skipComp(ves);
-			size_t idx2 = std.string.indexOf(ves, " ");
-			if( idx2 == -1 ) {
-				if( m_cmpA == "<=" || m_cmpA == "<" ) {
-					m_versA = Version(Version.RELEASE);
-					m_cmpB = m_cmpA;
-					m_cmpA = ">=";
-					m_versB = Version(ves);
-				}
-				else if( m_cmpA == ">=" || m_cmpA == ">" ) {
-					m_versA = Version(ves);
-					m_versB = Version(Version.HEAD);
-					m_cmpB = "<=";
-				}
-				else {
-					// Converts "==" to ">=a&&<=a", which makes merging easier
-					m_versA = m_versB = Version(ves);
-					m_cmpA = ">=";
-					m_cmpB = "<=";
-				}
-			} else {
-				assert(ves[idx2] == ' ');
-				m_versA = Version(ves[0..idx2]);
-				string v2 = ves[idx2+1..$];
-				m_cmpB = skipComp(v2);
-				m_versB = Version(v2);
-				
-				if( m_versB < m_versA ) {
-					swap(m_versA, m_versB);
-					swap(m_cmpA, m_cmpB);
-				}
-				enforce( m_cmpA != "==" && m_cmpB != "==", "For equality, please specify a single version.");
-			}
-		}
-	}
-
-	this(string cmp, string ver)
-	{
-		m_cmpA = cmp;
-		m_versB = m_versA = Version(ver);
-		m_cmpB = "==";
-	}
-	
-	this(const Dependency o) {
-		m_cmpA = o.m_cmpA; m_versA = Version(o.m_versA);
-		m_cmpB = o.m_cmpB; m_versB = Version(o.m_versB);
-		enforce( m_cmpA != "==" || m_cmpB == "==");
-		enforce(m_versA <= m_versB);
-	}
-	
-	override string toString() const {
-		string r;
-		// Special "==" case
-		if( m_versA == m_versB && m_cmpA == ">=" && m_cmpB == "<=" ){
-			if( m_versA == Version.MASTER ) r = "~master";
-			else r = "==" ~ to!string(m_versA);
-		} else {
-			if( m_versA != Version.RELEASE ) r = m_cmpA ~ to!string(m_versA);
-			if( m_versB != Version.HEAD ) r ~= (r.length==0?"" : " ") ~ m_cmpB ~ to!string(m_versB);
-			if( m_versA == Version.RELEASE && m_versB == Version.HEAD ) r = ">=0.0.0";
-		}
-		return r;
-	}
-
-	override bool opEquals(Object b)
-	{
-		if (this is b) return true; if (b is null) return false; if (typeid(this) != typeid(b)) return false;
-		Dependency o = cast(Dependency) b;
-		return o.m_cmpA == m_cmpA && o.m_cmpB == m_cmpB && o.m_versA == m_versA && o.m_versB == m_versB;
-	}
-	
-	bool valid() const {
-		return m_versA == m_versB // compare not important
-			|| (m_versA < m_versB && doCmp(m_cmpA, m_versB, m_versA) && doCmp(m_cmpB, m_versA, m_versB));
-	}
-	
-	bool matches(string vers) const { return matches(Version(vers)); }
-	bool matches(const(Version) v) const { return matches(v); }
-	bool matches(ref const(Version) v) const {
-		//logTrace(" try match: %s with: %s", v, this);
-		// Master only matches master
-		if(m_versA == Version.MASTER || v == Version.MASTER)
-			return m_versA == v;
-		if( !doCmp(m_cmpA, v, m_versA) )
-			return false;
-		if( !doCmp(m_cmpB, v, m_versB) )
-			return false;
-		return true;
-	}
-	
-	/// Merges to versions
-	Dependency merge(ref const(Dependency) o) const {
-		if(!valid())
-			return new Dependency(this);
-		if(!o.valid())
-			return new Dependency(o);
-		
-		Version a = m_versA > o.m_versA? Version(m_versA) : Version(o.m_versA);
-		Version b = m_versB < o.m_versB? Version(m_versB) : Version(o.m_versB);
-		
-		//logTrace(" this : %s", this);
-		//logTrace(" other: %s", o);
-	
-		Dependency d = new Dependency(this);
-		d.m_cmpA = !doCmp(m_cmpA, a,a)? m_cmpA : o.m_cmpA;
-		d.m_versA = a;
-		d.m_cmpB = !doCmp(m_cmpB, b,b)? m_cmpB : o.m_cmpB;
-		d.m_versB = b;
-		
-		//logTrace(" merged: %s", d);
-		
-		return d;
-	}
-	
-	private static bool isDigit(char ch) { return ch >= '0' && ch <= '9'; }
-	private static string skipComp(ref string c) {
-		size_t idx = 0;
-		while( idx < c.length && !isDigit(c[idx]) ) idx++;
-		enforce(idx < c.length, "Expected version number in version spec: "~c);
-		string cmp = idx==c.length-1||idx==0? ">=" : c[0..idx];
-		c = c[idx..$];
-		switch(cmp) {
-			default: enforce(false, "No/Unknown comparision specified: '"~cmp~"'"); return ">=";
-			case ">=": goto case; case ">": goto case;
-			case "<=": goto case; case "<": goto case;
-			case "==": return cmp;
-		}
-	}
-	
-	private static bool doCmp(string mthd, ref const Version a, ref const Version b) {
-		//logTrace("Calling %s%s%s", a, mthd, b);
-		switch(mthd) {
-			default: throw new Exception("Unknown comparison operator: "~mthd);
-			case ">": return a>b;
-			case ">=": return a>=b;
-			case "==": return a==b;
-			case "<=": return a<=b;
-			case "<": return a<b;
-		}
-	}
-}
-
-unittest {
-	Dependency a = new Dependency(">=1.1.0"), b = new Dependency(">=1.3.0");
-	assert( a.merge(b).valid() && to!string(a.merge(b)) == ">=1.3.0", to!string(a.merge(b)) );
-	
-	a = new Dependency("<=1.0.0 >=2.0.0");
-	assert( !a.valid(), to!string(a) );
-	
-	a = new Dependency(">=1.0.0 <=5.0.0"), b = new Dependency(">=2.0.0");
-	assert( a.merge(b).valid() && to!string(a.merge(b)) == ">=2.0.0 <=5.0.0", to!string(a.merge(b)) );
-	
-	try {
-		a = new Dependency(">1.0.0 ==5.0.0");
-		assert( false, "Construction is invalid");
-	} catch( Exception ) {}
-	
-	a = new Dependency(">1.0.0"), b = new Dependency("<2.0.0");
-	assert( a.merge(b).valid(), to!string(a.merge(b)));
-	assert( to!string(a.merge(b)) == ">1.0.0 <2.0.0", to!string(a.merge(b)) );
-	
-	a = new Dependency(">2.0.0"), b = new Dependency("<1.0.0");
-	assert( !(a.merge(b)).valid(), to!string(a.merge(b)));
-	
-	a = new Dependency(">=2.0.0"), b = new Dependency("<=1.0.0");
-	assert( !(a.merge(b)).valid(), to!string(a.merge(b)));
-	
-	a = new Dependency("==2.0.0"), b = new Dependency("==1.0.0");
-	assert( !(a.merge(b)).valid(), to!string(a.merge(b)));
-	
-	a = new Dependency("<=2.0.0"), b = new Dependency("==1.0.0");
-	Dependency m = a.merge(b);
-	assert( m.valid(), to!string(m));
-	assert( m.matches( Version("1.0.0") ) );
-	assert( !m.matches( Version("1.1.0") ) );
-	assert( !m.matches( Version("0.0.1") ) );
-}
-
-struct RequestedDependency {
-	this( string pkg, const Dependency de) {
-		dependency = new Dependency(de);
-		packages[pkg] = new Dependency(de);
-	}
-	Dependency dependency;
-	Dependency[string] packages;
-}
-
-class DependencyGraph {	
-	this(const Package root) {
-		m_root = root;
-		m_packages[m_root.name] = root;
-	}
-	
-	void insert(const Package p) {
-		enforce(p.name != m_root.name);
-		m_packages[p.name] = p;
-	}
-	
-	void remove(const Package p) {
-		enforce(p.name != m_root.name);
-		Rebindable!(const Package)* pkg = p.name in m_packages;
-		if( pkg ) m_packages.remove(p.name);
-	}
-	
-	private
-	{
-		alias Rebindable!(const Package) PkgType;
-	}
-	
-	void clearUnused() {
-		Rebindable!(const Package)[string] unused = m_packages.dup;
-		unused.remove(m_root.name);
-		forAllDependencies( (const PkgType* avail, string s, const Dependency d, const Package issuer) {
-			if(avail && d.matches(avail.vers))
-				unused.remove(avail.name);
-		});
-		foreach(string unusedPkg, d; unused) {
-			logTrace("Removed unused package: "~unusedPkg);
-			m_packages.remove(unusedPkg);
-		}
-	}
-	
-	RequestedDependency[string] conflicted() const {
-		RequestedDependency[string] deps = needed();
-		RequestedDependency[string] conflicts;
-		foreach(string pkg, d; deps)
-			if(!d.dependency.valid())
-				conflicts[pkg] = d;
-		return conflicts;
-	}
-	
-	RequestedDependency[string] missing() const {
-		RequestedDependency[string] deps;
-		forAllDependencies( (const PkgType* avail, string pkgId, const Dependency d, const Package issuer) {
-			if(!avail || !d.matches(avail.vers))
-				addDependency(deps, pkgId, d, issuer);
-		});
-		return deps;
-	}
-	
-	RequestedDependency[string] needed() const {
-		RequestedDependency[string] deps;
-		forAllDependencies( (const PkgType* avail, string pkgId, const Dependency d, const Package issuer) {
-			addDependency(deps, pkgId, d, issuer);
-		});
-		return deps;
-	}
-	
-	private void forAllDependencies(void delegate (const PkgType* avail, string pkgId, const Dependency d, const Package issuer) dg) const {
-		foreach(string issuerPackag, issuer; m_packages) {
-			foreach(string depPkg, dependency; issuer.dependencies) {
-				auto availPkg = depPkg in m_packages;
-				dg(availPkg, depPkg, dependency, issuer);
-			}
-		}
-	}
-	
-	private static void addDependency(ref RequestedDependency[string] deps, string packageId, const Dependency d, const Package issuer) {
-		logTrace("addDependency "~packageId~", '%s'", d);
-		auto d2 = packageId in deps;
-		if(!d2) {
-			deps[packageId] = RequestedDependency(issuer.name, d);
-		}
-		else {
-			d2.dependency = d2.dependency.merge(d);
-			d2.packages[issuer.name] = new Dependency(d);
-		}
-	}
-	
-	private {
-		const Package m_root;
-		PkgType[string] m_packages;
-	}
-}
\ No newline at end of file
+/**
+	Stuff with dependencies.
+
+	Copyright: © 2012 Matthias Dondorff
+	License: Subject to the terms of the MIT license, as written in the included LICENSE.txt file.
+	Authors: Matthias Dondorff, Sönke Ludwig
+*/
+module dub.dependency;
+
+import dub.utils;
+import dub.package_;
+
+import vibecompat.core.log;
+import vibecompat.core.file;
+import vibecompat.data.json;
+import vibecompat.inet.url;
+
+import std.array;
+import std.string;
+import std.exception;
+import std.algorithm;
+import std.typecons;
+import std.conv;
+static import std.compiler;
+
+
+/**
+	A version in the format "major.update.bugfix" or "~master", to identify trunk,
+	or "~branch_name" to identify a branch. Both Version types starting with "~"
+	refer to the head revision of the corresponding branch.
+*/
+struct Version {
+	static const Version RELEASE = Version("0.0.0");
+	static const Version HEAD = Version(to!string(MAX_VERS)~"."~to!string(MAX_VERS)~"."~to!string(MAX_VERS));
+	static const Version INVALID = Version();
+	static const Version MASTER = Version(MASTER_STRING);
+	static const string MASTER_STRING = "~master";
+	static immutable char BRANCH_IDENT = '~';
+	
+	private { 
+		static const size_t MAX_VERS = 9999;
+		static const size_t MASTER_VERS = cast(size_t)(-1);
+		string sVersion;
+	}
+	
+	this(string vers)
+	{
+		enforce(vers.length > 1);
+		enforce(vers[0] == BRANCH_IDENT || count(vers, ".") == 2);
+		sVersion = vers;
+		/*
+		if(vers == MASTER_STRING) {
+			v = [MASTER_VERS, MASTER_VERS, MASTER_VERS];
+		} else {
+			auto toks = split(vers, ".");
+			v.length = toks.length;
+			foreach( i, t; toks ) v[i] = t.to!size_t();
+		}
+		*/
+	}
+
+	this(const Version o)
+	{
+		sVersion = o.sVersion;
+	}
+	
+	bool opEquals(ref const Version oth) const { return sVersion == oth.sVersion; }
+	bool opEquals(const Version oth) const { return sVersion == oth.sVersion; }
+	
+	/// Returns true, if this version indicates a branch, which is not the trunk.
+	@property bool isBranch() const { return sVersion[0] == BRANCH_IDENT && sVersion != MASTER_STRING; }
+
+	/** 
+		Comparing Versions is generally possible, but comparing Versions 
+		identifying branches other than master will fail.
+	*/
+	int opCmp(ref const Version other)
+	const {
+		if(isBranch || other.isBranch) 
+			throw new Exception("Can't compare branch versions! (this: %s, other: %s)".format(this, other));
+
+		size_t v[] = toArray();
+		size_t ov[] = other.toArray();
+
+		foreach( i; 0 .. min(v.length, ov.length) )
+			if( v[i] != ov[i] )
+				return cast(int)v[i] - cast(int)ov[i];
+		return cast(int)v.length - cast(int)ov.length;
+	}
+	int opCmp(in Version other) const { return opCmp(other); }
+	
+	string toString() const { return sVersion; }
+
+	private size_t[] toArray() const { 
+		enforce(!isBranch, "Cannot convert a branch an array representation (%s)", sVersion);
+
+		size_t v[];
+		if(sVersion == MASTER_STRING) {
+			v = [MASTER_VERS, MASTER_VERS, MASTER_VERS];
+		} else {
+			auto toks = split(sVersion, ".");
+			v.length = toks.length;
+			foreach( i, t; toks ) v[i] = t.to!size_t();
+		}
+		return v;
+	}
+}
+
+unittest {
+	Version a, b;
+
+	try a = Version("1.0.0");
+	catch assert(false, "Constructing Version('1.0.0') failed");
+	assert(!a.isBranch, "Error: '1.0.0' treated as branch");
+	size_t[] arrRepr = [ 1, 0, 0 ];
+	assert(a.toArray == arrRepr, "Array representation of '1.0.0' is wrong.");
+	assert(a == a, "a == a failed");
+
+	try a = Version(Version.MASTER_STRING);
+	catch assert(false, "Constructing Version("~Version.MASTER_STRING~"') failed");
+	assert(!a.isBranch, "Error: '"~Version.MASTER_STRING~"' treated as branch");
+	arrRepr = [ Version.MASTER_VERS, Version.MASTER_VERS, Version.MASTER_VERS ];
+	assert(a.toArray == arrRepr, "Array representation of '"~Version.MASTER_STRING~"' is wrong.");
+	assert(a == Version.MASTER, "Constructed master version != default master version.");
+
+	try a = Version("~BRANCH");
+	catch assert(false, "Construction of branch Version failed.");
+	assert(a.isBranch, "Error: '~BRANCH' not treated as branch'");
+	try {
+		a.toArray();
+		assert(false, "Error: Converting branch version to array succeded.");
+	}
+	catch { /* exception expected */ }
+	assert(a == a, "a == a with branch failed");
+
+	// opCmp
+	a = Version("1.0.0");
+	b = Version("1.0.0");
+	assert(a == b, "a == b with a:'1.0.0', b:'1.0.0' failed");
+	b = Version("2.0.0");
+	assert(a != b, "a != b with a:'1.0.0', b:'2.0.0' failed");
+	a = Version(Version.MASTER_STRING);
+	b = Version("~BRANCH");
+	assert(a != b, "a != b with a:MASTER, b:'~branch' failed");
+}
+
+/// Representing a dependency, which is basically a version string and a 
+/// compare methode, e.g. '>=1.0.0 <2.0.0' (i.e. a space separates the two
+/// version numbers)
+class Dependency {
+	private {
+		string m_cmpA;
+		Version m_versA;
+		string m_cmpB;
+		Version m_versB;
+	}
+
+	this( string ves ) {
+		enforce( ves.length > 0);
+		string orig = ves;
+		if(ves[0] == Version.BRANCH_IDENT) {
+			m_cmpA = ">=";
+			m_cmpB = "<=";
+			m_versA = m_versB = Version(ves);
+		}
+		else {
+			m_cmpA = skipComp(ves);
+			size_t idx2 = std.string.indexOf(ves, " ");
+			if( idx2 == -1 ) {
+				if( m_cmpA == "<=" || m_cmpA == "<" ) {
+					m_versA = Version(Version.RELEASE);
+					m_cmpB = m_cmpA;
+					m_cmpA = ">=";
+					m_versB = Version(ves);
+				}
+				else if( m_cmpA == ">=" || m_cmpA == ">" ) {
+					m_versA = Version(ves);
+					m_versB = Version(Version.HEAD);
+					m_cmpB = "<=";
+				}
+				else {
+					// Converts "==" to ">=a&&<=a", which makes merging easier
+					m_versA = m_versB = Version(ves);
+					m_cmpA = ">=";
+					m_cmpB = "<=";
+				}
+			} else {
+				assert(ves[idx2] == ' ');
+				m_versA = Version(ves[0..idx2]);
+				string v2 = ves[idx2+1..$];
+				m_cmpB = skipComp(v2);
+				m_versB = Version(v2);
+
+				enforce(!m_versA.isBranch, "Partly a branch (A): %s", ves);
+				enforce(!m_versB.isBranch, "Partly a branch (B): %s", ves);
+
+				if( m_versB < m_versA ) {
+					swap(m_versA, m_versB);
+					swap(m_cmpA, m_cmpB);
+				}
+				enforce( m_cmpA != "==" && m_cmpB != "==", "For equality, please specify a single version.");
+			}
+		}
+	}
+
+	this(string cmp, string ver)
+	{
+		m_cmpA = cmp;
+		m_versB = m_versA = Version(ver);
+		m_cmpB = "==";
+	}
+	
+	this(const Dependency o) {
+		m_cmpA = o.m_cmpA; m_versA = Version(o.m_versA);
+		m_cmpB = o.m_cmpB; m_versB = Version(o.m_versB);
+		enforce( m_cmpA != "==" || m_cmpB == "==");
+		enforce(m_versA <= m_versB);
+	}
+	
+	override string toString() const {
+		string r;
+		// Special "==" case
+		if( m_versA == m_versB && m_cmpA == ">=" && m_cmpB == "<=" ){
+			if( m_versA == Version.MASTER ) r = "~master";
+			else r = "==" ~ to!string(m_versA);
+		} else {
+			if( m_versA != Version.RELEASE ) r = m_cmpA ~ to!string(m_versA);
+			if( m_versB != Version.HEAD ) r ~= (r.length==0?"" : " ") ~ m_cmpB ~ to!string(m_versB);
+			if( m_versA == Version.RELEASE && m_versB == Version.HEAD ) r = ">=0.0.0";
+		}
+		return r;
+	}
+
+	override bool opEquals(Object b)
+	{
+		if (this is b) return true; if (b is null) return false; if (typeid(this) != typeid(b)) return false;
+		Dependency o = cast(Dependency) b;
+		return o.m_cmpA == m_cmpA && o.m_cmpB == m_cmpB && o.m_versA == m_versA && o.m_versB == m_versB;
+	}
+	
+	bool valid() const {
+		return m_versA == m_versB // compare not important
+			|| (m_versA < m_versB && doCmp(m_cmpA, m_versB, m_versA) && doCmp(m_cmpB, m_versA, m_versB));
+	}
+	
+	bool matches(string vers) const { return matches(Version(vers)); }
+	bool matches(const(Version) v) const { return matches(v); }
+	bool matches(ref const(Version) v) const {
+		//logTrace(" try match: %s with: %s", v, this);
+		// Master only matches master
+		if(m_versA == Version.MASTER || m_versA.isBranch) {
+			enforce(m_versA == m_versB);
+			return m_versA == v;
+		}
+		if(v.isBranch)
+			return m_versA == v;
+		if(m_versA == Version.MASTER || v == Version.MASTER)
+			return m_versA == v;
+		if( !doCmp(m_cmpA, v, m_versA) )
+			return false;
+		if( !doCmp(m_cmpB, v, m_versB) )
+			return false;
+		return true;
+	}
+	
+	/// Merges to versions
+	Dependency merge(ref const(Dependency) o) const {
+		if(!valid())
+			return new Dependency(this);
+		if(!o.valid())
+			return new Dependency(o);
+		
+/// TODO: continue porting Version / Dependency to use branches and string
+
+		Version a = m_versA > o.m_versA? m_versA : o.m_versA;
+		Version b = m_versB < o.m_versB? m_versB : o.m_versB;
+		
+		//logTrace(" this : %s", this);
+		//logTrace(" other: %s", o);
+	
+		Dependency d = new Dependency(this);
+		d.m_cmpA = !doCmp(m_cmpA, a,a)? m_cmpA : o.m_cmpA;
+		d.m_versA = a;
+		d.m_cmpB = !doCmp(m_cmpB, b,b)? m_cmpB : o.m_cmpB;
+		d.m_versB = b;
+		
+		//logTrace(" merged: %s", d);
+		
+		return d;
+	}
+	
+	private static bool isDigit(char ch) { return ch >= '0' && ch <= '9'; }
+	private static string skipComp(ref string c) {
+		size_t idx = 0;
+		while( idx < c.length && !isDigit(c[idx]) ) idx++;
+		enforce(idx < c.length, "Expected version number in version spec: "~c);
+		string cmp = idx==c.length-1||idx==0? ">=" : c[0..idx];
+		c = c[idx..$];
+		switch(cmp) {
+			default: enforce(false, "No/Unknown comparision specified: '"~cmp~"'"); return ">=";
+			case ">=": goto case; case ">": goto case;
+			case "<=": goto case; case "<": goto case;
+			case "==": return cmp;
+		}
+	}
+	
+	private static bool doCmp(string mthd, ref const Version a, ref const Version b) {
+		//logTrace("Calling %s%s%s", a, mthd, b);
+		switch(mthd) {
+			default: throw new Exception("Unknown comparison operator: "~mthd);
+			case ">": return a>b;
+			case ">=": return a>=b;
+			case "==": return a==b;
+			case "<=": return a<=b;
+			case "<": return a<b;
+		}
+	}
+}
+
+unittest {
+	Dependency a = new Dependency(">=1.1.0"), b = new Dependency(">=1.3.0");
+	assert( a.merge(b).valid() && to!string(a.merge(b)) == ">=1.3.0", to!string(a.merge(b)) );
+	
+	a = new Dependency("<=1.0.0 >=2.0.0");
+	assert( !a.valid(), to!string(a) );
+	
+	a = new Dependency(">=1.0.0 <=5.0.0"), b = new Dependency(">=2.0.0");
+	assert( a.merge(b).valid() && to!string(a.merge(b)) == ">=2.0.0 <=5.0.0", to!string(a.merge(b)) );
+	
+	try {
+		a = new Dependency(">1.0.0 ==5.0.0");
+		assert( false, "Construction is invalid");
+	} catch( Exception ) {}
+	
+	a = new Dependency(">1.0.0"), b = new Dependency("<2.0.0");
+	assert( a.merge(b).valid(), to!string(a.merge(b)));
+	assert( to!string(a.merge(b)) == ">1.0.0 <2.0.0", to!string(a.merge(b)) );
+	
+	a = new Dependency(">2.0.0"), b = new Dependency("<1.0.0");
+	assert( !(a.merge(b)).valid(), to!string(a.merge(b)));
+	
+	a = new Dependency(">=2.0.0"), b = new Dependency("<=1.0.0");
+	assert( !(a.merge(b)).valid(), to!string(a.merge(b)));
+	
+	a = new Dependency("==2.0.0"), b = new Dependency("==1.0.0");
+	assert( !(a.merge(b)).valid(), to!string(a.merge(b)));
+	
+	a = new Dependency("<=2.0.0"), b = new Dependency("==1.0.0");
+	Dependency m = a.merge(b);
+	assert( m.valid(), to!string(m));
+	assert( m.matches( Version("1.0.0") ) );
+	assert( !m.matches( Version("1.1.0") ) );
+	assert( !m.matches( Version("0.0.1") ) );
+
+
+	// branches / head revisions
+	a = new Dependency(Version.MASTER_STRING);
+	assert(a.valid());
+	assert(a.matches(Version.MASTER));
+	b = new Dependency(Version.MASTER_STRING);
+	m = a.merge(b);
+	assert(m.matches(Version.MASTER));
+
+	try {
+		a = new Dependency(Version.MASTER_STRING ~ " <=1.0.0");
+		assert(false, "Construction invalid");
+	} catch { /*expected*/ }
+
+	try {
+		a = new Dependency(">=1.0.0 " ~ Version.MASTER_STRING);
+		assert(false, "Construction invalid");
+	} catch { /*expected*/ }
+
+	a = new Dependency(">=1.0.0");
+	b = new Dependency(Version.MASTER_STRING);
+
+	//// support crazy stuff like this?
+	//m = a.merge(b);
+	//assert(m.valid());
+	//assert(m.matches(Version.MASTER));
+
+	//b = new Dependency("~not_the_master");
+	//m = a.merge(b);
+//	assert(!m.valid());
+
+	immutable string branch1 = Version.BRANCH_IDENT ~ "Branch1";
+	immutable string branch2 = Version.BRANCH_IDENT ~ "Branch2";
+
+	try { 
+		a = new Dependency(branch1 ~ " " ~ branch2);
+		assert(false, "Error: '" ~ branch1 ~ " " ~ branch2 ~ "' succeeded");
+	} catch { /*expected*/ }
+	try { 
+		a = new Dependency(Version.MASTER_STRING ~ " " ~ branch1);
+		assert(false, "Error: '" ~ Version.MASTER_STRING ~ " " ~ branch1 ~ "' succeeded");
+	} catch { /*expected*/ }
+
+	a = new Dependency(branch1);
+	b = new Dependency(branch2);
+	try {
+		a.merge(b);
+		assert(false, "Shouldn't be able to merge to different branches");
+	} catch { /*expected*/ }
+	try {
+		b = a.merge(a);
+		assert(a == b);
+	}
+	catch assert(false, "Should be able to merge the same branches. (?)");
+
+
+	a = new Dependency(branch1);
+	assert(a.matches(branch1), "Dependency(branch1) does not match 'branch1'");
+	assert(a.matches(Version(branch1)), "Dependency(branch1) does not match Version('branch1')");
+	assert(!a.matches(Version.MASTER), "Dependency(branch1) matches Version.MASTER");
+	assert(!a.matches(branch2), "Dependency(branch1) matches 'branch2'");
+	assert(!a.matches(Version("1.0.0")), "Dependency(branch1) matches '1.0.0'");
+	a = new Dependency(">=1.0.0");
+	assert(!a.matches(Version(branch1)), "Dependency(1.0.0) matches 'branch1'");
+
+	logTrace("Dependency Unittest sucess.");
+}
+
+struct RequestedDependency {
+	this( string pkg, const Dependency de) {
+		dependency = new Dependency(de);
+		packages[pkg] = new Dependency(de);
+	}
+	Dependency dependency;
+	Dependency[string] packages;
+}
+
+class DependencyGraph {	
+	this(const Package root) {
+		m_root = root;
+		m_packages[m_root.name] = root;
+	}
+	
+	void insert(const Package p) {
+		enforce(p.name != m_root.name);
+		m_packages[p.name] = p;
+	}
+	
+	void remove(const Package p) {
+		enforce(p.name != m_root.name);
+		Rebindable!(const Package)* pkg = p.name in m_packages;
+		if( pkg ) m_packages.remove(p.name);
+	}
+	
+	private
+	{
+		alias Rebindable!(const Package) PkgType;
+	}
+	
+	void clearUnused() {
+		Rebindable!(const Package)[string] unused = m_packages.dup;
+		unused.remove(m_root.name);
+		forAllDependencies( (const PkgType* avail, string s, const Dependency d, const Package issuer) {
+			if(avail && d.matches(avail.vers))
+				unused.remove(avail.name);
+		});
+		foreach(string unusedPkg, d; unused) {
+			logTrace("Removed unused package: "~unusedPkg);
+			m_packages.remove(unusedPkg);
+		}
+	}
+	
+	RequestedDependency[string] conflicted() const {
+		RequestedDependency[string] deps = needed();
+		RequestedDependency[string] conflicts;
+		foreach(string pkg, d; deps)
+			if(!d.dependency.valid())
+				conflicts[pkg] = d;
+		return conflicts;
+	}
+	
+	RequestedDependency[string] missing() const {
+		RequestedDependency[string] deps;
+		forAllDependencies( (const PkgType* avail, string pkgId, const Dependency d, const Package issuer) {
+			if(!avail || !d.matches(avail.vers))
+				addDependency(deps, pkgId, d, issuer);
+		});
+		return deps;
+	}
+	
+	RequestedDependency[string] needed() const {
+		RequestedDependency[string] deps;
+		forAllDependencies( (const PkgType* avail, string pkgId, const Dependency d, const Package issuer) {
+			addDependency(deps, pkgId, d, issuer);
+		});
+		return deps;
+	}
+	
+	private void forAllDependencies(void delegate (const PkgType* avail, string pkgId, const Dependency d, const Package issuer) dg) const {
+		foreach(string issuerPackag, issuer; m_packages) {
+			foreach(string depPkg, dependency; issuer.dependencies) {
+				auto availPkg = depPkg in m_packages;
+				dg(availPkg, depPkg, dependency, issuer);
+			}
+		}
+	}
+	
+	private static void addDependency(ref RequestedDependency[string] deps, string packageId, const Dependency d, const Package issuer) {
+		logTrace("addDependency "~packageId~", '%s'", d);
+		auto d2 = packageId in deps;
+		if(!d2) {
+			deps[packageId] = RequestedDependency(issuer.name, d);
+		}
+		else {
+			d2.dependency = d2.dependency.merge(d);
+			d2.packages[issuer.name] = new Dependency(d);
+		}
+	}
+	
+	private {
+		const Package m_root;
+		PkgType[string] m_packages;
+	}
+}
+
+unittest {
+	/*
+		
+	*/
+
+}