diff --git a/crates/ail/tests/typeclass_22b3.rs b/crates/ail/tests/typeclass_22b3.rs
index e874075..6b4a626 100644
--- a/crates/ail/tests/typeclass_22b3.rs
+++ b/crates/ail/tests/typeclass_22b3.rs
@@ -442,3 +442,37 @@ fn fixpoint_handles_chained_class_method_calls() {
          — multi-round fixpoint property"
     );
 }
+
+/// After the mono pass, the body of `main` in
+/// test_22b2_instance_present must reference `show#Int` instead
+/// of `show`.
+#[test]
+fn rewrite_replaces_class_method_var_with_mono_symbol_same_module() {
+    let entry = examples_dir().join("test_22b2_instance_present.ail.json");
+    let ws = ailang_core::load_workspace(&entry).expect("load");
+    let diags = ailang_check::check_workspace(&ws);
+    assert!(diags.is_empty(), "fixture must typecheck: {:?}", diags);
+
+    let ws = ailang_check::monomorphise_workspace(&ws).expect("mono");
+
+    let main_module = ws.modules.get("test_22b2_instance_present").unwrap();
+    let main_fn = main_module
+        .defs
+        .iter()
+        .find_map(|d| match d {
+            ailang_core::ast::Def::Fn(f) if f.name == "main" => Some(f),
+            _ => None,
+        })
+        .expect("main");
+
+    // The body is `App { fn: Var "show", args: [Lit 42] }`. After
+    // rewrite, the callee Var must be `show#Int`.
+    let callee_name: &str = match &main_fn.body {
+        ailang_core::ast::Term::App { callee, .. } => match callee.as_ref() {
+            ailang_core::ast::Term::Var { name } => name.as_str(),
+            other => panic!("callee is not Var: {:?}", other),
+        },
+        other => panic!("body is not App: {:?}", other),
+    };
+    assert_eq!(callee_name, "show#Int");
+}
diff --git a/crates/ailang-check/src/mono.rs b/crates/ailang-check/src/mono.rs
index 28ecce3..3e9bfd4 100644
--- a/crates/ailang-check/src/mono.rs
+++ b/crates/ailang-check/src/mono.rs
@@ -51,7 +51,7 @@
 //! the implementation so the constraint is visible to anyone
 //! extending the skeleton.
 
-use ailang_core::ast::{ClassDef, Def, FnDef as AstFnDef, InstanceDef, Term, Type};
+use ailang_core::ast::{Arm, ClassDef, Def, FnDef as AstFnDef, InstanceDef, Term, Type};
 use ailang_core::workspace::Workspace;
 use crate::Result;
 use indexmap::IndexMap;
@@ -148,6 +148,71 @@ pub fn monomorphise_workspace(ws: &Workspace) -> Result<Workspace> {
         }
     }
 
+    // Phase 3: rewrite call sites in every fn / const body. Walk in
+    // the same pre-order as collect_residuals_ordered so the cursor
+    // and the per-callsite target list align position-by-position.
+    let env = build_workspace_env(&ws_owned); // re-build: ws_owned has new defs.
+    let module_names: Vec<String> = ws_owned.modules.keys().cloned().collect();
+    for mname in &module_names {
+        let n_defs = ws_owned.modules[mname].defs.len();
+        for i in 0..n_defs {
+            let (ordered, defining_module_name): (Vec<Option<MonoTarget>>, String) = {
+                let m = &ws_owned.modules[mname];
+                let d = &m.defs[i];
+                match d {
+                    Def::Fn(f) => (collect_residuals_ordered(f, mname, &env)?, mname.clone()),
+                    Def::Const(c) => {
+                        let pseudo = AstFnDef {
+                            name: c.name.clone(),
+                            ty: c.ty.clone(),
+                            params: Vec::new(),
+                            body: c.value.clone(),
+                            doc: None,
+                            suppress: Vec::new(),
+                        };
+                        (collect_residuals_ordered(&pseudo, mname, &env)?, mname.clone())
+                    }
+                    _ => continue,
+                }
+            };
+            let m = ws_owned.modules.get_mut(mname).unwrap();
+            let d = &mut m.defs[i];
+            let ordered_concrete: Vec<MonoTarget> = ordered
+                .into_iter()
+                .map(|o| {
+                    o.unwrap_or_else(|| MonoTarget {
+                        class: String::new(),
+                        method: String::new(),
+                        type_: Type::unit(),
+                        defining_module: defining_module_name.clone(),
+                    })
+                })
+                .collect();
+            let mut cursor = 0usize;
+            match d {
+                Def::Fn(f) => {
+                    rewrite_class_method_calls(
+                        &mut f.body,
+                        &env.class_methods,
+                        mname,
+                        &ordered_concrete,
+                        &mut cursor,
+                    );
+                }
+                Def::Const(c) => {
+                    rewrite_class_method_calls(
+                        &mut c.value,
+                        &env.class_methods,
+                        mname,
+                        &ordered_concrete,
+                        &mut cursor,
+                    );
+                }
+                _ => {}
+            }
+        }
+    }
+
     Ok(ws_owned)
 }
 
@@ -502,3 +567,167 @@ pub fn synthesise_mono_fn(
         suppress: Vec::new(),
     })
 }
+
+/// Iter 22b.3: rewrite every class-method call site in `body` to
+/// the corresponding mono symbol, using `ordered_targets` —
+/// the per-call-site resolved targets collected by a parallel
+/// synth-replay run on the same body.
+///
+/// The walker increments a positional counter at each
+/// class-method-named `Term::Var` it encounters. The counter must
+/// match the order in which `synth` pushes residuals (pre-order
+/// AST walk; child evaluation order matches the `match` arms in
+/// `crate::synth`). When this invariant holds, `ordered_targets[idx]`
+/// is the target resolved at the i-th class-method call site.
+///
+/// `caller_module`: name of the module enclosing this body. If
+/// the target's `defining_module` differs, the rewritten name is
+/// qualified `<defining_module>.<mono_symbol>` (cross-module
+/// resolution path); otherwise unqualified. Targets whose `class`
+/// is empty are sentinel placeholders for non-concrete residuals
+/// — the cursor advances over them and the name is left unchanged.
+fn rewrite_class_method_calls(
+    body: &mut Term,
+    class_methods: &BTreeMap<String, crate::ClassMethodEntry>,
+    caller_module: &str,
+    ordered_targets: &[MonoTarget],
+    cursor: &mut usize,
+) {
+    match body {
+        Term::Var { name } => {
+            if class_methods.contains_key(name) {
+                if let Some(t) = ordered_targets.get(*cursor) {
+                    if !t.class.is_empty() {
+                        let sym = mono_symbol(&t.method, &t.type_);
+                        let new_name = if t.defining_module == caller_module {
+                            sym
+                        } else {
+                            format!("{}.{}", t.defining_module, sym)
+                        };
+                        *name = new_name;
+                    }
+                    // else: residual was non-concrete → leave name unchanged.
+                }
+                *cursor += 1;
+            }
+        }
+        Term::App { callee, args, .. } => {
+            rewrite_class_method_calls(callee, class_methods, caller_module, ordered_targets, cursor);
+            for a in args {
+                rewrite_class_method_calls(a, class_methods, caller_module, ordered_targets, cursor);
+            }
+        }
+        Term::Let { value, body, .. } => {
+            rewrite_class_method_calls(value, class_methods, caller_module, ordered_targets, cursor);
+            rewrite_class_method_calls(body, class_methods, caller_module, ordered_targets, cursor);
+        }
+        Term::LetRec { body, in_term, .. } => {
+            rewrite_class_method_calls(body, class_methods, caller_module, ordered_targets, cursor);
+            rewrite_class_method_calls(in_term, class_methods, caller_module, ordered_targets, cursor);
+        }
+        Term::If { cond, then, else_ } => {
+            rewrite_class_method_calls(cond, class_methods, caller_module, ordered_targets, cursor);
+            rewrite_class_method_calls(then, class_methods, caller_module, ordered_targets, cursor);
+            rewrite_class_method_calls(else_, class_methods, caller_module, ordered_targets, cursor);
+        }
+        Term::Do { args, .. } => {
+            for a in args {
+                rewrite_class_method_calls(a, class_methods, caller_module, ordered_targets, cursor);
+            }
+        }
+        Term::Ctor { args, .. } => {
+            for a in args {
+                rewrite_class_method_calls(a, class_methods, caller_module, ordered_targets, cursor);
+            }
+        }
+        Term::Match { scrutinee, arms } => {
+            rewrite_class_method_calls(scrutinee, class_methods, caller_module, ordered_targets, cursor);
+            for Arm { body, .. } in arms {
+                rewrite_class_method_calls(body, class_methods, caller_module, ordered_targets, cursor);
+            }
+        }
+        Term::Lam { body, .. } => {
+            rewrite_class_method_calls(body, class_methods, caller_module, ordered_targets, cursor);
+        }
+        Term::Seq { lhs, rhs } => {
+            rewrite_class_method_calls(lhs, class_methods, caller_module, ordered_targets, cursor);
+            rewrite_class_method_calls(rhs, class_methods, caller_module, ordered_targets, cursor);
+        }
+        Term::Clone { value } => {
+            rewrite_class_method_calls(value, class_methods, caller_module, ordered_targets, cursor);
+        }
+        Term::ReuseAs { source, body } => {
+            rewrite_class_method_calls(source, class_methods, caller_module, ordered_targets, cursor);
+            rewrite_class_method_calls(body, class_methods, caller_module, ordered_targets, cursor);
+        }
+        Term::Lit { .. } => {}
+    }
+}
+
+/// Iter 22b.3: traversal-ordered residual collection — used by
+/// the rewrite walker to align cursor positions. Unlike
+/// [`collect_mono_targets`], this includes non-concrete residuals
+/// as `None`, preserving one-entry-per-callsite alignment.
+pub(crate) fn collect_residuals_ordered(
+    f: &AstFnDef,
+    module_name: &str,
+    env: &crate::Env,
+) -> Result<Vec<Option<MonoTarget>>> {
+    let (rigids, inner_ty): (Vec<String>, Type) = match &f.ty {
+        Type::Forall { vars, constraints: _, body } => (vars.clone(), (**body).clone()),
+        other => (vec![], other.clone()),
+    };
+    let param_tys: Vec<Type> = match &inner_ty {
+        Type::Fn { params, .. } => params.clone(),
+        _ => return Ok(Vec::new()),
+    };
+
+    let mut env = env.clone();
+    for v in &rigids {
+        env.rigid_vars.insert(v.clone());
+    }
+    env.current_module = module_name.to_string();
+
+    let mut locals: IndexMap<String, Type> = IndexMap::new();
+    for (n, t) in f.params.iter().zip(param_tys.iter()) {
+        locals.insert(n.clone(), t.clone());
+    }
+    let mut effects: BTreeSet<String> = BTreeSet::new();
+    let mut subst = crate::Subst::default();
+    let mut counter: u32 = 0;
+    let mut residuals: Vec<crate::ResidualConstraint> = Vec::new();
+    crate::synth(
+        &f.body,
+        &env,
+        &mut locals,
+        &mut effects,
+        &f.name,
+        &mut subst,
+        &mut counter,
+        &mut residuals,
+    )?;
+
+    let mut out: Vec<Option<MonoTarget>> = Vec::new();
+    for r in residuals {
+        let r_ty = subst.apply(&r.type_);
+        if !crate::is_fully_concrete(&r_ty) {
+            out.push(None);
+            continue;
+        }
+        let key = (r.class.clone(), ailang_core::canonical::type_hash(&r_ty));
+        let entry = match env.workspace_registry.entries.get(&key) {
+            Some(e) => e,
+            None => {
+                out.push(None);
+                continue;
+            }
+        };
+        out.push(Some(MonoTarget {
+            class: r.class.clone(),
+            method: r.method.clone(),
+            type_: r_ty,
+            defining_module: entry.defining_module.clone(),
+        }));
+    }
+    Ok(out)
+}
diff --git a/examples/test_22b2_instance_present.ail.json b/examples/test_22b2_instance_present.ail.json
index 9090b86..1b6634a 100644
--- a/examples/test_22b2_instance_present.ail.json
+++ b/examples/test_22b2_instance_present.ail.json
@@ -19,7 +19,13 @@
       "type": { "k": "con", "name": "Int" },
       "methods": [{
         "name": "show",
-        "body": { "t": "lit", "lit": { "kind": "str", "value": "n" } }
+        "body": {
+          "t": "lam",
+          "params": ["x"],
+          "paramTypes": [{ "k": "var", "name": "a" }],
+          "retType": { "k": "con", "name": "Str" },
+          "body": { "t": "lit", "lit": { "kind": "str", "value": "n" } }
+        }
       }]
     },
     {