diff --git a/src/common.rs b/src/common.rs
new file mode 100644
index 0000000000000000000000000000000000000000..09c7b444324f49055bac3e5a20295aa631e94054
--- /dev/null
+++ b/src/common.rs
@@ -0,0 +1,115 @@
+///////////////////// PRELUDE /////////////////////
+
+pub use core::{
+    cmp::Ordering,
+    fmt::Debug,
+    hash::{Hash, Hasher},
+    ops::{Range, RangeFrom},
+    time::Duration,
+};
+pub use indexmap::{IndexMap, IndexSet};
+pub use maplit::{hashmap, hashset};
+pub use mio::{
+    net::{TcpListener, TcpStream},
+    Event, Evented, Events, Poll, PollOpt, Ready, Token,
+};
+pub use std::{
+    collections::{hash_map::Entry, BTreeMap, HashMap, HashSet},
+    convert::TryInto,
+    net::SocketAddr,
+    sync::Arc,
+    time::Instant,
+};
+pub use Polarity::*;
+
+///////////////////// DEFS /////////////////////
+
+pub type Payload = Vec<u8>;
+pub type ControllerId = u32;
+pub type ChannelIndex = u32;
+
+/// This is a unique identifier for a channel (i.e., port).
+#[derive(Debug, Eq, PartialEq, Clone, Hash, Copy, Ord, PartialOrd)]
+pub struct ChannelId {
+    pub(crate) controller_id: ControllerId,
+    pub(crate) channel_index: ChannelIndex,
+}
+
+#[derive(Debug, Eq, PartialEq, Clone, Hash, Copy, Ord, PartialOrd)]
+pub enum Polarity {
+    Putter, // output port (from the perspective of the component)
+    Getter, // input port (from the perspective of the component)
+}
+
+#[derive(Eq, PartialEq, Ord, PartialOrd, Hash, Copy, Clone, Debug)]
+pub struct Key(u64);
+
+pub trait ProtocolDescription: Sized {
+    type S: ComponentState<D = Self>;
+
+    fn parse(pdl: &[u8]) -> Result<Self, String>;
+    fn main_interface_polarities(&self) -> Vec<Polarity>;
+    fn new_main_component(&self, interface: &[Key]) -> Self::S;
+}
+
+pub trait ComponentState: Sized + Clone {
+    type D: ProtocolDescription;
+    fn pre_sync_run<C: MonoContext<D = Self::D, S = Self>>(
+        &mut self,
+        runtime_ctx: &mut C,
+        protocol_description: &Self::D,
+    ) -> MonoBlocker;
+
+    fn sync_run<C: PolyContext<D = Self::D>>(
+        &mut self,
+        runtime_ctx: &mut C,
+        protocol_description: &Self::D,
+    ) -> PolyBlocker;
+}
+
+#[derive(Debug, Clone)]
+pub enum MonoBlocker {
+    Inconsistent,
+    ComponentExit,
+    SyncBlockStart,
+}
+
+#[derive(Debug, Clone)]
+pub enum PolyBlocker {
+    Inconsistent,
+    SyncBlockEnd,
+    CouldntReadMsg(Key),
+    CouldntCheckFiring(Key),
+    PutMsg(Key, Payload),
+}
+
+pub trait MonoContext {
+    type D: ProtocolDescription;
+    type S: ComponentState<D = Self::D>;
+
+    fn new_component(&mut self, moved_keys: HashSet<Key>, init_state: Self::S);
+    fn new_channel(&mut self) -> [Key; 2];
+    fn new_random(&self) -> u64;
+}
+pub trait PolyContext {
+    type D: ProtocolDescription;
+
+    fn is_firing(&self, ekey: Key) -> Option<bool>;
+    fn read_msg(&self, ekey: Key) -> Option<&Payload>;
+}
+
+///////////////////// IMPL /////////////////////
+impl Key {
+    pub fn from_raw(raw: u64) -> Self {
+        Self(raw)
+    }
+    pub fn to_raw(self) -> u64 {
+        self.0
+    }
+    pub fn to_token(self) -> mio::Token {
+        mio::Token(self.0.try_into().unwrap())
+    }
+    pub fn from_token(t: mio::Token) -> Self {
+        Self(t.0.try_into().unwrap())
+    }
+}