diff --git a/Cargo.lock b/Cargo.lock
index 3c914bb..92d1ee3 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -77,6 +77,7 @@ dependencies = [
  "quote",
  "semver",
  "sha3",
+ "thiserror",
 ]
 
 [[package]]
@@ -283,6 +284,26 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "thiserror"
+version = "2.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c006c85c7651b3cf2ada4584faa36773bd07bac24acfb39f3c431b36d7e667aa"
+dependencies = [
+ "thiserror-impl",
+]
+
+[[package]]
+name = "thiserror-impl"
+version = "2.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f077553d607adc1caf65430528a576c757a71ed73944b66ebb58ef2bbd243568"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "typenum"
 version = "1.17.0"
diff --git a/bok-macro/src/lib.rs b/bok-macro/src/lib.rs
index 588ec74..c24716b 100644
--- a/bok-macro/src/lib.rs
+++ b/bok-macro/src/lib.rs
@@ -42,7 +42,7 @@ pub fn repository(attrs: TokenStream, input: TokenStream) -> TokenStream {
             }
 
             quote! {
-                #[derive(::bok::Repository)]
+                #[derive(::bok::Repository, Debug)]
                 #ast
             }
             .into()
diff --git a/bok/Cargo.toml b/bok/Cargo.toml
index 33b4624..9f46424 100644
--- a/bok/Cargo.toml
+++ b/bok/Cargo.toml
@@ -21,3 +21,4 @@ proc-macro2 = "1.0"
 quote = "1.0"
 semver = { version = "1.0" }
 sha3 = { version = "0.10" }
+thiserror = { version = "2.0" }
diff --git a/bok/src/collection.rs b/bok/src/collection.rs
index 358c896..75bce07 100644
--- a/bok/src/collection.rs
+++ b/bok/src/collection.rs
@@ -16,29 +16,99 @@
  */
 
 use ::std::{
-    collections::HashMap,
+    collections::BTreeMap,
     sync::{Arc, RwLock},
     vec::Vec,
 };
 
+use crate::{Path, Pkg, PkgName, RepoName, Repository};
+
+#[derive(Debug, ::thiserror::Error)]
+pub enum Error {
+    #[error("package already present")]
+    AlreadyPresent((Arc<dyn Repository>, ArcLock<dyn Pkg>)),
+    #[error("not found")]
+    NotFound,
+}
+
 type ArcLock<T> = Arc<RwLock<T>>;
-type PkgMap = HashMap<crate::PkgName, ArcLock<dyn crate::Pkg>>;
+type PkgMap = BTreeMap<Path<PkgName>, (Arc<dyn Repository>, ArcLock<dyn Pkg>)>;
 
 /// Collection of packages, subset of what is present on one repository only
 pub struct Collection {
-    repos: RwLock<Vec<ArcLock<dyn crate::Repository>>>,
-    pkgs: RwLock<PkgMap>,
-    repos_pkgs: RwLock<HashMap<crate::RepoName, PkgMap>>,
-    //repos_pkgs: RwLock<HashMap<crate::Repository, PkgMap>>,
+    repos: RwLock<Vec<Arc<dyn Repository>>>,
+    repos_pkgs: RwLock<BTreeMap<Path<RepoName>, PkgMap>>,
 }
 
 impl Collection {
+    /// Create a new empty collection of pkgs
     pub fn new() -> Collection {
-        const PKGNUM: usize = 512;
         Collection {
             repos: RwLock::new(Vec::with_capacity(8)),
-            pkgs: RwLock::new(HashMap::with_capacity(PKGNUM)),
-            repos_pkgs: RwLock::new(HashMap::with_capacity(PKGNUM)),
+            repos_pkgs: RwLock::new(BTreeMap::new()),
+        }
+    }
+    pub fn add_pkg(
+        &self,
+        r: Arc<dyn Repository>,
+        p: ArcLock<dyn Pkg>,
+    ) -> Result<(), Error> {
+        let repo_name = r.path();
+        let mut repos = self.repos.write().unwrap();
+        let mut repos_pkgs = self.repos_pkgs.write().unwrap();
+        if repos
+            .binary_search_by(|x| x.path().cmp(&repo_name))
+            .is_err()
+        {
+            repos.push(r.clone());
+            repos.sort_by(|a, b| a.path().cmp(&b.path()))
+        }
+        let pkg_name = p.read().unwrap().path();
+        match repos_pkgs.get_mut(&repo_name) {
+            Some(pkg_map) => match pkg_map.get(&pkg_name) {
+                Some((r, p)) => {
+                    return Err(Error::AlreadyPresent((r.clone(), p.clone())));
+                }
+                None => {
+                    pkg_map.insert(pkg_name, (r, p));
+                }
+            },
+            None => {
+                let mut pkg_map: PkgMap = BTreeMap::new();
+                pkg_map.insert(pkg_name, (r, p));
+                repos_pkgs.insert(repo_name, pkg_map);
+            }
+        }
+
+        Ok(())
+    }
+    pub fn find(
+        &self,
+        pkg_path: Path<PkgName>,
+    ) -> Result<(Arc<dyn Repository>, ArcLock<dyn Pkg>), Error> {
+        let repos_pkgs = self.repos_pkgs.read().unwrap();
+        for (_, pkg_map) in repos_pkgs.iter() {
+            match pkg_map.get(&pkg_path) {
+                Some((r, p)) => {
+                    return Ok((r.clone(), p.clone()));
+                }
+                None => {}
+            }
+        }
+        Err(Error::NotFound)
+    }
+    pub fn find_in_repo(
+        &self,
+        repo_path: Path<RepoName>,
+        pkg_path: Path<PkgName>,
+    ) -> Result<(Arc<dyn Repository>, ArcLock<dyn Pkg>), Error> {
+        let repos_pkgs = self.repos_pkgs.read().unwrap();
+        match repos_pkgs.get(&repo_path) {
+            None => Err(Error::NotFound),
+            Some(pkg_map) => match pkg_map.get(&pkg_path) {
+                Some((r, p)) => Ok((r.clone(), p.clone())),
+                None => Err(Error::NotFound),
+            },
         }
     }
 }
diff --git a/bok/src/lib.rs b/bok/src/lib.rs
index bbe129c..1ddfd1a 100644
--- a/bok/src/lib.rs
+++ b/bok/src/lib.rs
@@ -86,13 +86,13 @@ macro_rules! packages {
 }
 
 /// Marks your struct as a repository
-pub trait Repository {
+pub trait Repository: ::std::fmt::Debug {
     fn name(&self) -> RepoName;
     fn path(&self) -> Path<RepoName>;
 }
 
 /// This is an empty Package List.
-#[derive(::std::default::Default)]
+#[derive(::std::default::Default, Debug)]
 pub struct RepositoryEmpty {}
 impl Repository for RepositoryEmpty {
     fn name(&self) -> RepoName {
diff --git a/bok/src/names.rs b/bok/src/names.rs
index 0c15ddd..f9d6e0b 100644
--- a/bok/src/names.rs
+++ b/bok/src/names.rs
@@ -82,24 +82,6 @@ where
     }
 }
 
-/// Marks your struct as a repository
-pub trait Repository {
-    fn name(&self) -> RepoName;
-    fn path(&self) -> Path<RepoName>;
-}
-
-/// This is an empty Package List.
-#[derive(::std::default::Default)]
-pub struct RepositoryEmpty {}
-impl Repository for RepositoryEmpty {
-    fn name(&self) -> RepoName {
-        "RepositoryEmpty".into()
-    }
-    fn path(&self) -> Path<RepoName> {
-        Path::new("::bok::RepositoryEmpty")
-    }
-}
-
 /// Strong typedef for a package name
 #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone)]
 pub struct PkgName(pub String);