diff --git a/compiler/erg_compiler/context/inquire.rs b/compiler/erg_compiler/context/inquire.rs
index de770c16..73279a66 100644
--- a/compiler/erg_compiler/context/inquire.rs
+++ b/compiler/erg_compiler/context/inquire.rs
@@ -1566,11 +1566,14 @@ impl Context {
     // -> K.variance() == vec![Contravariant, Covariant]
     // TODO: support keyword arguments
     pub(crate) fn type_params_variance(&self) -> Vec<Variance> {
+        let match_tp_name = |tp: &TyParam, name: &VarName| -> bool {
+            tp.qual_name().as_ref() == Some(name.inspect())
+        };
         let in_inout = |t: &Type, name: &VarName| {
             (&t.qual_name()[..] == "Input" || &t.qual_name()[..] == "Output")
                 && t.typarams()
                     .first()
-                    .map(|inner| inner.qual_name().as_ref() == Some(name.inspect()))
+                    .map(|inner| match_tp_name(inner, name))
                     .unwrap_or(false)
         };
         self.params
@@ -1578,13 +1581,13 @@ impl Context {
             .map(|(opt_name, _)| {
                 if let Some(name) = opt_name {
                     // トレイトの変性を調べるときはsuper_classesも見る必要がある
-                    if let Some(t) = self
+                    if let Some(variance_trait) = self
                         .super_traits
                         .iter()
                         .chain(self.super_classes.iter())
                         .find(|t| in_inout(t, name))
                     {
-                        match &t.qual_name()[..] {
+                        match &variance_trait.qual_name()[..] {
                             "Output" => Variance::Covariant,
                             "Input" => Variance::Contravariant,
                             _ => unreachable!(),
diff --git a/compiler/erg_compiler/context/tyvar.rs b/compiler/erg_compiler/context/tyvar.rs
index 0968be45..b15da51e 100644
--- a/compiler/erg_compiler/context/tyvar.rs
+++ b/compiler/erg_compiler/context/tyvar.rs
@@ -18,7 +18,7 @@ use crate::ty::{HasType, Predicate, Type};
 // use crate::context::eval::SubstContext;
 use crate::context::{Context, Variance};
 use crate::error::{SingleTyCheckResult, TyCheckError, TyCheckErrors, TyCheckResult};
-use crate::{feature_error, hir, type_feature_error};
+use crate::{feature_error, hir, type_feature_error, unreachable_error};
 
 use Predicate as Pred;
 use Type::*;
@@ -1438,17 +1438,12 @@ impl Context {
                         // * sub_unify({0},   ?T(:> {1},   <: Nat)): (?T(:> {0, 1}, <: Nat))
                         // * sub_unify(Bool,  ?T(<: Bool or Y)): (?T == Bool)
                         Constraint::Sandwiched { sub, sup } => {
-                            /*if let Some(new_sub) = self.max(maybe_sub, sub) {
-                                *constraint =
-                                    Constraint::new_sandwiched(new_sub.clone(), mem::take(sup), *cyclicity);
-                            } else {*/
                             let new_sub = self.union(maybe_sub, sub);
                             if sup.contains_union(&new_sub) {
                                 rfv.link(&new_sub); // Bool <: ?T <: Bool or Y ==> ?T == Bool
                             } else {
                                 *constraint = Constraint::new_sandwiched(new_sub, mem::take(sup));
                             }
-                            // }
                         }
                         // sub_unify(Nat, ?T(: Type)): (/* ?T(:> Nat) */)
                         Constraint::TypeOf(ty) => {
@@ -1705,7 +1700,8 @@ impl Context {
                     self.sub_unify_pred(sub_first, sup_first, loc)?;
                     return Ok(());
                 }
-                todo!("{sub}, {sup}")
+                log!(err "unification error: {sub} <: {sup}");
+                unreachable_error!(TyCheckErrors, TyCheckError, self)
             }
             // {I: Int | I >= 1} <: Nat == {I: Int | I >= 0}
             (Type::Refinement(_), sup) => {
diff --git a/compiler/erg_compiler/ty/typaram.rs b/compiler/erg_compiler/ty/typaram.rs
index 6bf3ddf1..42594cb3 100644
--- a/compiler/erg_compiler/ty/typaram.rs
+++ b/compiler/erg_compiler/ty/typaram.rs
@@ -310,10 +310,10 @@ impl LimitedDisplay for TyParam {
 
 impl CanbeFree for TyParam {
     fn unbound_name(&self) -> Option<Str> {
-        if let TyParam::FreeVar(fv) = self {
-            fv.unbound_name()
-        } else {
-            None
+        match self {
+            TyParam::FreeVar(fv) => fv.unbound_name(),
+            TyParam::Type(t) => t.unbound_name(),
+            _ => None,
         }
     }