diff --git a/Cargo.toml b/Cargo.toml
index 11b68a5..1396507 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,3 +14,5 @@ crate-type = ["cdylib", "rlib"]
 anyhow = "1.0.75"
 nom = "7.1.3"
 pyo3 = "0.19.2"
+serde = { version = "1.0.188", features = ["derive"] }
+serde_yaml = "0.9.25"
diff --git a/src/lib.rs b/src/lib.rs
index 336d944..2924921 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,6 +5,7 @@
 #![warn(clippy::redundant_closure_for_method_calls)]
 #![warn(let_underscore_drop)]
 
+mod list;
 mod refs;
 
 use pyo3::prelude::*;
diff --git a/src/list/mod.rs b/src/list/mod.rs
new file mode 100644
index 0000000..264c5b5
--- /dev/null
+++ b/src/list/mod.rs
@@ -0,0 +1,22 @@
+mod removable;
+mod unique;
+
+/// Defines the shared interface between the unique list (which is effectively an insert-ordered
+/// Set) and the unique list which supports removals.
+pub trait List {
+    fn new() -> Self;
+    fn with_capacity(capacity: usize) -> Self;
+    fn len(&self) -> usize;
+    fn shrink_to_fit(&mut self);
+    fn append_if_new(&mut self, item: String);
+    fn merge(&mut self, other: Self);
+    fn merge_from(&mut self, other: &Self);
+}
+
+/// Returns the 0-indexed position of the item in the list, if it's found
+fn item_pos(items: &[String], item: &String) -> Option<usize> {
+    items.iter().position(|v| v == item)
+}
+
+pub use removable::*;
+pub use unique::*;
diff --git a/src/list/removable.rs b/src/list/removable.rs
new file mode 100644
index 0000000..9662fe0
--- /dev/null
+++ b/src/list/removable.rs
@@ -0,0 +1,369 @@
+use serde::Deserialize;
+
+use super::{item_pos, List};
+
+#[derive(Clone, Debug, Default, Deserialize, Eq, PartialEq)]
+#[serde(from = "Vec<String>")]
+pub struct RemovableList {
+    items: Vec<String>,
+    #[serde(skip)]
+    negations: Vec<String>,
+}
+
+impl RemovableList {
+    /// Handles negating the provided item
+    ///
+    /// Assumes that the negation prefix is already stripped from `negitem`
+    fn handle_negation(&mut self, negitem: String) {
+        if let Some(itpos) = item_pos(&self.items, &negitem) {
+            // ...remove item from our list if it's negated in other
+            self.items.remove(itpos);
+        } else if item_pos(&self.negations, &negitem).is_none() {
+            // ...remember negations which we haven't processed yet and
+            // which aren't present in self.
+            self.negations.push(negitem);
+        }
+    }
+
+    /// Internal merge implementation which takes negations into account
+    ///
+    /// Used by List::merge/List::merge_from
+    fn merge_impl(
+        &mut self,
+        itemiter: impl Iterator<Item = String>,
+        negiter: impl Iterator<Item = String>,
+    ) {
+        // merge negations first...
+        for n in negiter {
+            self.handle_negation(n);
+        }
+        // take items from other and append them using append_if_new
+        for it in itemiter {
+            self.append_if_new(it);
+        }
+    }
+}
+
+impl From<Vec<String>> for RemovableList {
+    #[inline]
+    fn from(item: Vec<String>) -> Self {
+        let mut res = RemovableList {
+            items: vec![],
+            negations: vec![],
+        };
+        for it in item {
+            res.append_if_new(it);
+        }
+        res
+    }
+}
+
+impl From<RemovableList> for Vec<String> {
+    #[inline]
+    fn from(l: RemovableList) -> Self {
+        l.items
+    }
+}
+
+impl List for RemovableList {
+    #[inline]
+    fn new() -> Self {
+        Self::default()
+    }
+
+    #[inline]
+    fn with_capacity(capacity: usize) -> Self {
+        Self {
+            items: Vec::with_capacity(capacity),
+            negations: vec![],
+        }
+    }
+
+    #[inline]
+    fn len(&self) -> usize {
+        self.items.len()
+    }
+
+    #[inline]
+    fn shrink_to_fit(&mut self) {
+        self.items.shrink_to_fit();
+        self.negations.shrink_to_fit();
+    }
+
+    /// Appends or removes item from list
+    ///
+    /// Regular strings are inserted in the list if they're not present yet. When `item` is
+    /// prefixed with ~ it's removed from the list if present.  Negated items which can't be
+    /// removed immediately are stored as negations, for later processing.
+    fn append_if_new(&mut self, item: String) {
+        if let Some(neg) = item.strip_prefix('~') {
+            // handle negation
+            self.handle_negation(neg.to_string());
+        } else if let Some(negpos) = item_pos(&self.negations, &item) {
+            // Remove previously negated item from negations list instead of
+            // inserting it into the list.
+            self.negations.remove(negpos);
+        } else if item_pos(&self.items, &item).is_none() {
+            // Finally, insert item if neither condition applies and the item
+            // isn't present in the list yet.
+            self.items.push(item);
+        };
+    }
+
+    /// Merges other into self, consuming other
+    ///
+    /// Negations from other are processed first, removing items which are already present from our
+    /// list. Negations which weren't processed are kept and merged into the list's negations.
+    /// Afterwards all items in other are taken and appended if they're not present in our list.
+    fn merge(&mut self, other: Self) {
+        self.merge_impl(other.items.into_iter(), other.negations.into_iter());
+    }
+
+    /// Merges other into self, creating a clone of other
+    fn merge_from(&mut self, other: &Self) {
+        self.merge_impl(other.items.iter().cloned(), other.negations.iter().cloned());
+    }
+}
+
+#[cfg(test)]
+mod removable_list_tests {
+    use super::*;
+
+    fn make_abc() -> RemovableList {
+        vec!["a".into(), "b".into(), "c".into()].into()
+    }
+
+    fn make_def() -> RemovableList {
+        vec!["d".into(), "e".into(), "f".into()].into()
+    }
+
+    #[test]
+    fn test_list_to_vec() {
+        let mut list = RemovableList::default();
+        list.append_if_new("a".into());
+        list.append_if_new("b".into());
+        list.append_if_new("c".into());
+        list.append_if_new("d".into());
+        list.append_if_new("b".into());
+        list.append_if_new("~d".into());
+
+        let vec: Vec<String> = vec!["a".into(), "b".into(), "c".into()];
+
+        let intoed: Vec<String> = list.clone().into();
+
+        assert_eq!(intoed, vec);
+        assert_eq!(Vec::from(list), vec);
+    }
+
+    #[test]
+    fn test_vec_to_list() {
+        let vec: Vec<String> = vec![
+            "a".into(),
+            "b".into(),
+            "c".into(),
+            "d".into(),
+            "b".into(),
+            "~d".into(),
+            "~e".into(),
+        ];
+        let mut list = RemovableList::default();
+        list.append_if_new("a".into());
+        list.append_if_new("b".into());
+        list.append_if_new("c".into());
+        list.append_if_new("d".into());
+        list.append_if_new("b".into());
+        list.append_if_new("~d".into());
+        list.append_if_new("~e".into());
+
+        let intoed: RemovableList = vec.clone().into();
+
+        assert_eq!(intoed, list);
+        assert_eq!(RemovableList::from(vec), list);
+    }
+
+    #[test]
+    fn test_list_add_new() {
+        let mut l = make_abc();
+        l.append_if_new("d".into());
+        let expected: Vec<String> = vec!["a".into(), "b".into(), "c".into(), "d".into()];
+        assert_eq!(l.items, expected);
+        assert_eq!(l.negations, Vec::<String>::new());
+    }
+
+    #[test]
+    fn test_list_add_existing() {
+        let mut l = make_abc();
+        l.append_if_new("c".into());
+        let expected: Vec<String> = vec!["a".into(), "b".into(), "c".into()];
+        assert_eq!(l.items, expected);
+        assert_eq!(l.negations, Vec::<String>::new());
+    }
+
+    #[test]
+    fn test_list_remove_nonexisting() {
+        let mut l = make_abc();
+        l.append_if_new("~d".into());
+        let expected: Vec<String> = vec!["a".into(), "b".into(), "c".into()];
+        assert_eq!(l.items, expected);
+        assert_eq!(l.negations, vec!["d".to_string()]);
+    }
+
+    #[test]
+    fn test_list_remove_existing() {
+        let mut l = make_abc();
+        l.append_if_new("~b".into());
+        let expected: Vec<String> = vec!["a".into(), "c".into()];
+        assert_eq!(l.items, expected);
+        assert_eq!(l.negations, Vec::<String>::new());
+    }
+
+    #[test]
+    fn test_list_negate_then_add() {
+        let mut l = make_abc();
+        l.append_if_new("~d".into());
+        l.append_if_new("d".into());
+        let expected: Vec<String> = vec!["a".into(), "b".into(), "c".into()];
+        assert_eq!(l.items, expected);
+        assert_eq!(l.negations, Vec::<String>::new());
+    }
+
+    #[test]
+    fn test_list_negate_then_negate() {
+        let mut l = make_abc();
+        l.append_if_new("~d".into());
+        l.append_if_new("~d".into());
+        let expected: Vec<String> = vec!["a".into(), "b".into(), "c".into()];
+        assert_eq!(l.items, expected);
+        assert_eq!(l.negations, vec!["d".to_string()]);
+    }
+
+    #[test]
+    fn test_merge() {
+        let mut l = make_abc();
+        let o = make_def();
+        l.merge(o);
+
+        assert_eq!(
+            l.items,
+            vec![
+                "a".to_string(),
+                "b".to_string(),
+                "c".to_string(),
+                "d".to_string(),
+                "e".to_string(),
+                "f".to_string()
+            ]
+        );
+        assert_eq!(l.negations, Vec::<String>::new());
+    }
+
+    #[test]
+    fn test_merge_same() {
+        let mut l = make_abc();
+        let o = make_abc();
+        l.merge(o);
+
+        assert_eq!(
+            l.items,
+            vec!["a".to_string(), "b".to_string(), "c".to_string(),]
+        );
+        assert_eq!(l.negations, Vec::<String>::new());
+    }
+
+    #[test]
+    fn test_merge_add_and_remove() {
+        let mut l = make_abc();
+        let mut o: RemovableList = vec!["d".into()].into();
+        o.append_if_new("~c".into());
+        l.merge(o);
+
+        assert_eq!(
+            l.items,
+            vec!["a".to_string(), "b".to_string(), "d".to_string()]
+        );
+        assert_eq!(l.negations, Vec::<String>::new());
+    }
+
+    #[test]
+    fn test_merge_add_store_removal() {
+        let mut l = make_abc();
+        let mut o: RemovableList = vec!["d".into()].into();
+        o.append_if_new("~c".into());
+        o.append_if_new("~e".into());
+        l.merge(o);
+
+        assert_eq!(
+            l.items,
+            vec!["a".to_string(), "b".to_string(), "d".to_string()]
+        );
+        assert_eq!(l.negations, vec!["e".to_string()]);
+    }
+
+    #[test]
+    fn test_merge_add_apply_removal() {
+        let mut l = make_abc();
+        l.append_if_new("~d".into());
+        let o: RemovableList = vec!["d".into()].into();
+        l.merge(o);
+
+        assert_eq!(
+            l.items,
+            vec!["a".to_string(), "b".to_string(), "c".to_string()]
+        );
+        assert_eq!(l.negations, Vec::<String>::new());
+    }
+
+    #[test]
+    fn test_merge_add_store_unique() {
+        let mut l = make_abc();
+        l.append_if_new("~d".into());
+        let mut o = RemovableList::default();
+        o.append_if_new("~d".into());
+        l.merge(o);
+
+        assert_eq!(
+            l.items,
+            vec!["a".to_string(), "b".to_string(), "c".to_string()]
+        );
+        assert_eq!(l.negations, vec!["d".to_string()]);
+    }
+
+    #[test]
+    fn test_deserialize_process_negations() {
+        let yaml = r#"
+        - a
+        - b
+        - ~b
+        "#;
+        let l: RemovableList = serde_yaml::from_str(yaml).unwrap();
+
+        assert_eq!(l.items, vec!["a".to_string()]);
+        assert_eq!(l.negations, Vec::<String>::new());
+    }
+
+    #[test]
+    fn test_deserialize_remove_duplicates() {
+        let yaml = r#"
+        - a
+        - a
+        - b
+        "#;
+        let l: RemovableList = serde_yaml::from_str(yaml).unwrap();
+
+        assert_eq!(l.items, vec!["a".to_string(), "b".to_string()]);
+        assert_eq!(l.negations, Vec::<String>::new());
+    }
+
+    #[test]
+    fn test_deserialize_store_negations() {
+        let yaml = r#"
+        - a
+        - b
+        - ~c
+        "#;
+        let l: RemovableList = serde_yaml::from_str(yaml).unwrap();
+
+        assert_eq!(l.items, vec!["a".to_string(), "b".to_string()]);
+        assert_eq!(l.negations, vec!["c".to_string()]);
+    }
+}
diff --git a/src/list/unique.rs b/src/list/unique.rs
new file mode 100644
index 0000000..8f57e04
--- /dev/null
+++ b/src/list/unique.rs
@@ -0,0 +1,184 @@
+use serde::Deserialize;
+
+use super::{item_pos, List};
+
+#[derive(Clone, Debug, Default, Deserialize, Eq, PartialEq)]
+#[serde(from = "Vec<String>")]
+pub struct UniqueList {
+    items: Vec<String>,
+}
+
+impl UniqueList {
+    pub fn items_iter(&self) -> impl Iterator<Item = &String> {
+        self.items.iter()
+    }
+
+    #[cfg(test)]
+    pub fn get_items(&self) -> &Vec<String> {
+        &self.items
+    }
+
+    fn merge_impl(&mut self, itemiter: impl Iterator<Item = String>) {
+        for it in itemiter {
+            self.append_if_new(it);
+        }
+    }
+}
+
+impl From<Vec<String>> for UniqueList {
+    #[inline]
+    fn from(item: Vec<String>) -> Self {
+        let mut res = Self { items: vec![] };
+        for it in item {
+            res.append_if_new(it);
+        }
+        res
+    }
+}
+
+impl From<UniqueList> for Vec<String> {
+    #[inline]
+    fn from(l: UniqueList) -> Self {
+        l.items
+    }
+}
+
+impl List for UniqueList {
+    #[inline]
+    fn new() -> Self {
+        Self::default()
+    }
+
+    #[inline]
+    fn with_capacity(capacity: usize) -> Self {
+        Self {
+            items: Vec::with_capacity(capacity),
+        }
+    }
+
+    #[inline]
+    fn len(&self) -> usize {
+        self.items.len()
+    }
+
+    #[inline]
+    fn shrink_to_fit(&mut self) {
+        self.items.shrink_to_fit();
+    }
+
+    /// Appends item to list if it's not present yet
+    fn append_if_new(&mut self, item: String) {
+        if item_pos(&self.items, &item).is_none() {
+            self.items.push(item);
+        }
+    }
+
+    /// Merges other into self, consuming other
+    fn merge(&mut self, other: Self) {
+        self.merge_impl(other.items.into_iter());
+    }
+
+    /// Merges other into self, creating a clone of other
+    fn merge_from(&mut self, other: &Self) {
+        self.merge_impl(other.items.iter().cloned());
+    }
+}
+
+#[cfg(test)]
+mod unique_list_tests {
+    use super::*;
+
+    #[test]
+    fn test_list_to_vec() {
+        let mut list = UniqueList::default();
+        list.append_if_new("a".into());
+        list.append_if_new("b".into());
+        list.append_if_new("c".into());
+        list.append_if_new("b".into());
+
+        let vec: Vec<String> = vec!["a".into(), "b".into(), "c".into()];
+
+        let intoed: Vec<String> = list.clone().into();
+
+        assert_eq!(intoed, vec);
+        assert_eq!(Vec::from(list), vec);
+    }
+
+    #[test]
+    fn test_vec_to_list() {
+        let vec: Vec<String> = vec!["a".into(), "b".into(), "c".into(), "d".into(), "b".into()];
+        let mut list = UniqueList::default();
+        list.append_if_new("a".into());
+        list.append_if_new("b".into());
+        list.append_if_new("c".into());
+        list.append_if_new("d".into());
+        list.append_if_new("b".into());
+
+        let intoed: UniqueList = vec.clone().into();
+
+        assert_eq!(intoed, list);
+        assert_eq!(UniqueList::from(vec), list);
+    }
+
+    #[test]
+    fn test_add_new() {
+        let mut l = UniqueList::default();
+        l.append_if_new("a".into());
+        let r: Vec<String> = l.into();
+        assert_eq!(r, vec!["a".to_string()]);
+    }
+
+    #[test]
+    fn test_add_unique() {
+        let mut l = UniqueList::default();
+        l.append_if_new("a".into());
+        l.append_if_new("a".into());
+        let r: Vec<String> = l.into();
+        assert_eq!(r, vec!["a".to_string()]);
+    }
+
+    #[test]
+    fn test_merge() {
+        let mut a: UniqueList = vec!["a".into()].into();
+        let b: UniqueList = vec!["b".into()].into();
+
+        a.merge(b);
+
+        let r: Vec<String> = a.into();
+        assert_eq!(r, vec!["a".to_string(), "b".to_string()]);
+    }
+
+    #[test]
+    fn test_merge_unique_append() {
+        let mut a: UniqueList = vec!["b".into(), "a".into()].into();
+        let b: UniqueList = vec!["b".into()].into();
+
+        a.merge(b);
+
+        let r: Vec<String> = a.into();
+        assert_eq!(r, vec!["b".to_string(), "a".to_string()]);
+    }
+
+    #[test]
+    fn test_deserialize() {
+        let yaml = r#"
+        - a
+        - b
+        "#;
+        let l: UniqueList = serde_yaml::from_str(yaml).unwrap();
+
+        assert_eq!(l.items, vec!["a".to_string(), "b".to_string()]);
+    }
+
+    #[test]
+    fn test_deserialize_unique() {
+        let yaml = r#"
+        - a
+        - b
+        - a
+        "#;
+        let l: UniqueList = serde_yaml::from_str(yaml).unwrap();
+
+        assert_eq!(l.items, vec!["a".to_string(), "b".to_string()]);
+    }
+}