diff --git a/package/origlang-cli/src/args.rs b/package/origlang-cli/src/args.rs
index c2cc612a..7dce5529 100644
--- a/package/origlang-cli/src/args.rs
+++ b/package/origlang-cli/src/args.rs
@@ -98,7 +98,6 @@ pub enum EmitPhase {
     LexerToken,
     Ast,
     TypedAst,
-    Ir0,
     Ir1,
     Ir2,
 }
diff --git a/package/origlang-cli/src/task/emit.rs b/package/origlang-cli/src/task/emit.rs
index be147bb2..71d903eb 100644
--- a/package/origlang-cli/src/task/emit.rs
+++ b/package/origlang-cli/src/task/emit.rs
@@ -73,15 +73,6 @@ impl Task for UnstableEmit {
 
         let the_lower = TheTranspiler::new(optimizer);
 
-        if self.phase == EmitPhase::Ir0 {
-            let ir_sequence = the_lower.optimizer().optimize(ir_sequence);
-
-            println!("{ir_sequence:#?}");
-            return Ok(())
-        }
-
-        let ir_sequence = the_lower.lower(ir_sequence);
-
         if self.phase == EmitPhase::Ir1 {
             let ir_sequence: Vec<IR1> = the_lower.optimizer().optimize(ir_sequence);
 
diff --git a/package/origlang-cli/src/task/interpret.rs b/package/origlang-cli/src/task/interpret.rs
index d79d433d..f92c2a20 100644
--- a/package/origlang-cli/src/task/interpret.rs
+++ b/package/origlang-cli/src/task/interpret.rs
@@ -33,8 +33,7 @@ impl Task for Interpret {
         let transpiler = TheTranspiler::new(&NoOptimization);
         let ir = root_ast.into_ir();
         let ir = transpiler.lower(ir);
-        let ir = transpiler.lower(ir);
-        runtime.start(ir);
+        runtime.start(&ir);
         eprintln!("runtime.run: {:?}", i.elapsed());
         Ok(())
     }
diff --git a/package/origlang-cli/src/task/repl.rs b/package/origlang-cli/src/task/repl.rs
index cee2fc19..ce90980a 100644
--- a/package/origlang-cli/src/task/repl.rs
+++ b/package/origlang-cli/src/task/repl.rs
@@ -31,8 +31,6 @@ impl Repl {
     fn naive_lower(tra: TypedRootAst) -> Vec<IR2> {
         let ir = tra.into_ir();
         let trans = TheTranspiler::new(&NoOptimization);
-        let ir = trans.lower(ir);
-        
 
         trans.lower(ir)
     }
@@ -64,7 +62,7 @@ impl Task for Repl {
             match parser.parse() {
                 Ok(ast) => {
                     let ast = checker.check(ast)?;
-                    runtime.start(Self::naive_lower(ast));
+                    runtime.start(&Self::naive_lower(ast));
                 }
                 Err(error_message) => {
                     let error = error_message.kind;
diff --git a/package/origlang-compiler-entrypoint/src/lib.rs b/package/origlang-compiler-entrypoint/src/lib.rs
index d51270a5..e47a1712 100644
--- a/package/origlang-compiler-entrypoint/src/lib.rs
+++ b/package/origlang-compiler-entrypoint/src/lib.rs
@@ -11,7 +11,7 @@ use origlang_compiler::parser::{Parser, SimpleErrorWithPos};
 use origlang_compiler::type_check::error::TypeCheckError;
 use origlang_compiler::type_check::TypeChecker;
 use origlang_diagnostics::{Diagnostic, DiagnosticSink};
-use origlang_ir::{IntoVerbatimSequencedIR, IR0, IR1, IR2};
+use origlang_ir::{IntoVerbatimSequencedIR, IR1, IR2};
 use origlang_ir_optimizer::lower::{LowerStep, TheTranspiler};
 use origlang_ir_optimizer::preset::{NoOptimization, OptimizationPreset};
 
@@ -63,7 +63,7 @@ impl TheCompiler {
             optimization_preset: &self.optimization_preset
         };
 
-        let ir1_seq = the_transpiler.lower(ir0_seq);
+        let ir1_seq = ir0_seq;
         let (pre, post): (Vec<_>, Vec<_>) =
             self.scanner.ir1_scanner.iter().partition(|x| matches!(x, PreOrPost::Pre(..)));
 
@@ -146,7 +146,6 @@ pub trait Scanner<T> {
 }
 
 pub struct OptimizationPresetCollection {
-    pub ir0: Box<dyn OptimizationPreset<IR0>>,
     pub ir1: Box<dyn OptimizationPreset<IR1>>,
     pub ir2: Box<dyn OptimizationPreset<IR2>>,
 }
@@ -154,7 +153,6 @@ pub struct OptimizationPresetCollection {
 impl OptimizationPresetCollection {
     fn none() -> Self {
         Self {
-            ir0: Box::new(NoOptimization) as Box<_>,
             ir1: Box::new(NoOptimization) as Box<_>,
             ir2: Box::new(NoOptimization) as Box<_>,
         }
@@ -171,6 +169,5 @@ macro_rules! delegate_optimization_to_field {
     };
 }
 
-delegate_optimization_to_field!(ir0, IR0);
 delegate_optimization_to_field!(ir1, IR1);
 delegate_optimization_to_field!(ir2, IR2);
diff --git a/package/origlang-interop/src/lib.rs b/package/origlang-interop/src/lib.rs
index d051e0bb..e5592aa8 100644
--- a/package/origlang-interop/src/lib.rs
+++ b/package/origlang-interop/src/lib.rs
@@ -121,9 +121,8 @@ pub fn run() {
                     let lower = typed_root.into_ir();
                     let _ = Timer::new("runtime.ir.lower");
                     let lower = transpiler.lower(lower);
-                    let lower = transpiler.lower(lower);
                     let _ = Timer::new("runtime.start");
-                    runtime.start(lower);
+                    runtime.start(&lower);
                 }
 
                 Ok(())
diff --git a/package/origlang-ir-optimizer/src/ir0.rs b/package/origlang-ir-optimizer/src/ir0.rs
deleted file mode 100644
index 6c1faff5..00000000
--- a/package/origlang-ir-optimizer/src/ir0.rs
+++ /dev/null
@@ -1,12 +0,0 @@
-use origlang_ir::IR0;
-
-pub struct EliminateAfterExit(pub Vec<IR0>);
-
-impl EliminateAfterExit {
-    #[must_use = "return value is optimized IR, dropping it will waste it"]
-    pub fn optimize(self) -> Vec<IR0> {
-        let mut x = self.0.into_iter().take_while(|x| *x != IR0::Exit).collect::<Vec<_>>();
-        x.push(IR0::Exit);
-        x
-    }
-}
diff --git a/package/origlang-ir-optimizer/src/ir1.rs b/package/origlang-ir-optimizer/src/ir1.rs
index 227bc8a9..a6a85bac 100644
--- a/package/origlang-ir-optimizer/src/ir1.rs
+++ b/package/origlang-ir-optimizer/src/ir1.rs
@@ -307,4 +307,15 @@ impl InlineSimpleBlock {
             other => other,
         }
     }
-}
\ No newline at end of file
+}
+
+pub struct EliminateAfterExit(pub Vec<IR1>);
+
+impl EliminateAfterExit {
+    #[must_use = "return value is optimized IR, dropping it will waste it"]
+    pub fn optimize(self) -> Vec<IR1> {
+        let mut x = self.0.into_iter().take_while(|x| *x != IR1::Exit).collect::<Vec<_>>();
+        x.push(IR1::Exit);
+        x
+    }
+}
diff --git a/package/origlang-ir-optimizer/src/ir1/tests.rs b/package/origlang-ir-optimizer/src/ir1/tests.rs
index 09f854c5..019c6189 100644
--- a/package/origlang-ir-optimizer/src/ir1/tests.rs
+++ b/package/origlang-ir-optimizer/src/ir1/tests.rs
@@ -1,7 +1,7 @@
 use origlang_ast::after_parse::BinaryOperatorKind;
 use origlang_ir::IR1;
 use origlang_typesystem_model::{Type, TypedExpression, TypedIntLiteral};
-use crate::ir1::{FoldBinaryOperatorInvocationWithConstant, FoldIfWithConstantCondition, InlineSimpleBlock};
+use crate::ir1::{EliminateAfterExit, FoldBinaryOperatorInvocationWithConstant, FoldIfWithConstantCondition, InlineSimpleBlock};
 
 #[test]
 fn fold_binary_operator_is_recursive() {
@@ -84,3 +84,12 @@ fn inline_simple_block() {
     ])
 }
 
+#[test]
+fn cut_down_after_exit() {
+    let opt_output = EliminateAfterExit(vec![
+        IR1::Exit,
+        IR1::Output(TypedExpression::BooleanLiteral(false))
+    ]).optimize();
+
+    assert_eq!(opt_output, [ IR1::Exit ]);
+}
diff --git a/package/origlang-ir-optimizer/src/lib.rs b/package/origlang-ir-optimizer/src/lib.rs
index 59593691..3c05786b 100644
--- a/package/origlang-ir-optimizer/src/lib.rs
+++ b/package/origlang-ir-optimizer/src/lib.rs
@@ -1,7 +1,6 @@
 #![deny(clippy::all, clippy::panicking_unwrap, clippy::panic)]
 #![warn(clippy::pedantic, clippy::nursery)]
 
-pub mod ir0;
 pub mod ir1;
 pub mod preset;
 pub mod lower;
diff --git a/package/origlang-ir-optimizer/src/lower.rs b/package/origlang-ir-optimizer/src/lower.rs
index d7f1c1ec..cc995fa6 100644
--- a/package/origlang-ir-optimizer/src/lower.rs
+++ b/package/origlang-ir-optimizer/src/lower.rs
@@ -1,4 +1,4 @@
-use origlang_ir::{CompiledTypedExpression, IntoVerbatimSequencedIR, IR0, IR1, IR2};
+use origlang_ir::{CompiledTypedExpression, IntoVerbatimSequencedIR, IR1, IR2};
 use origlang_typesystem_model::{TypedExpression, TypedStatement};
 use crate::preset::OptimizationPreset;
 
@@ -19,9 +19,9 @@ impl<'t> TheTranspiler<'t> {
     }
 }
 
-pub trait EachStep: OptimizationPreset<IR0> + OptimizationPreset<IR1> + OptimizationPreset<IR2> {}
+pub trait EachStep: OptimizationPreset<IR1> + OptimizationPreset<IR2> {}
 
-impl<T: OptimizationPreset<IR0> + OptimizationPreset<IR1> + OptimizationPreset<IR2> + ?Sized> EachStep for T {}
+impl<T: OptimizationPreset<IR1> + OptimizationPreset<IR2> + ?Sized> EachStep for T {}
 
 impl TheTranspiler<'_> {
     fn compile_typed_expression(&self, te: TypedExpression) -> CompiledTypedExpression {
@@ -62,9 +62,7 @@ impl TheTranspiler<'_> {
     }
 
     fn compile_typed_statement(&self, ts: TypedStatement) -> Vec<IR2> {
-        let opt_ir0 = self.optimization_preset.optimize(ts.into_ir());
-        let ir1 = self.lower(opt_ir0);
-        let opt_ir1 = OptimizationPreset::<IR1>::optimize(self.optimization_preset, ir1);
+        let opt_ir1 = OptimizationPreset::<IR1>::optimize(self.optimization_preset, ts.into_ir());
         let ir2 = self.lower(opt_ir1);
 
         OptimizationPreset::<IR2>::optimize(self.optimization_preset, ir2)
@@ -75,16 +73,6 @@ pub trait LowerStep<From, To> {
     fn lower(&self, ir: Vec<From>) -> Vec<To>;
 }
 
-impl LowerStep<IR0, IR1> for TheTranspiler<'_> {
-    fn lower(&self, ir: Vec<IR0>) -> Vec<IR1> {
-        // TODO: this sequence is always terminated by IR0::Exit. Should be reflected on the type.
-        ir.into_iter().map(|x| match x {
-            IR0::Normal(ir1) => ir1,
-            IR0::Exit => IR1::Exit,
-        }).collect()
-    }
-}
-
 impl LowerStep<IR1, IR2> for TheTranspiler<'_> {
     fn lower(&self, ir: Vec<IR1>) -> Vec<IR2> {
         ir.into_iter().map(|x| match x {
diff --git a/package/origlang-ir-optimizer/src/preset.rs b/package/origlang-ir-optimizer/src/preset.rs
index 5cf96174..8a6e1451 100644
--- a/package/origlang-ir-optimizer/src/preset.rs
+++ b/package/origlang-ir-optimizer/src/preset.rs
@@ -1,5 +1,5 @@
 use tap::Pipe;
-use origlang_ir::{IR0, IR1, IR2};
+use origlang_ir::{IR1, IR2};
 
 pub trait OptimizationPreset<IR> {
     /// 最適化をする。
@@ -13,23 +13,13 @@ pub trait OptimizationPreset<IR> {
 /// Do not perform optimization at all.
 pub struct NoOptimization;
 
-impl OptimizationPreset<IR0> for NoOptimization {
-    #[allow(clippy::redundant_closure_for_method_calls)]
-    fn optimize(&self, seq: Vec<IR0>) -> Vec<IR0> {
-        #[allow(clippy::wildcard_imports)]
-        use crate::ir0::*;
-
-        seq
-            .pipe(EliminateAfterExit).pipe(|x| x.optimize())
-    }
-}
-
 impl OptimizationPreset<IR1> for NoOptimization {
     fn optimize(&self, seq: Vec<IR1>) -> Vec<IR1> {
         #[allow(unused_imports)]
         use crate::ir1::*;
 
         seq
+            .pipe(EliminateAfterExit).pipe(|x| x.optimize())
     }
 }
 
@@ -42,17 +32,6 @@ impl OptimizationPreset<IR2> for NoOptimization {
 /// Enables some basic optimization.
 pub struct SimpleOptimization;
 
-impl OptimizationPreset<IR0> for SimpleOptimization {
-    #[allow(clippy::redundant_closure_for_method_calls)]
-    fn optimize(&self, seq: Vec<IR0>) -> Vec<IR0> {
-        #[allow(clippy::wildcard_imports)]
-        use crate::ir0::*;
-
-        seq
-            .pipe(EliminateAfterExit).pipe(|x| x.optimize())
-    }
-}
-
 impl OptimizationPreset<IR1> for SimpleOptimization {
     #[allow(clippy::redundant_closure_for_method_calls)]
     fn optimize(&self, seq: Vec<IR1>) -> Vec<IR1> {
@@ -63,6 +42,7 @@ impl OptimizationPreset<IR1> for SimpleOptimization {
             .pipe(FoldBinaryOperatorInvocationWithConstant).pipe(|x| x.optimize())
             .pipe(FoldIfWithConstantCondition).pipe(|x| x.optimize())
             .pipe(InlineSimpleBlock).pipe(|x| x.optimize())
+            .pipe(EliminateAfterExit).pipe(|x| x.optimize())
     }
 }
 
diff --git a/package/origlang-ir/src/lib.rs b/package/origlang-ir/src/lib.rs
index 71e3fa9b..6169386d 100644
--- a/package/origlang-ir/src/lib.rs
+++ b/package/origlang-ir/src/lib.rs
@@ -6,38 +6,24 @@ use origlang_ast::after_parse::BinaryOperatorKind;
 use origlang_ast::Identifier;
 use origlang_typesystem_model::{Type, TypedExpression, TypedIntLiteral, TypedRootAst, TypedStatement};
 
-/// The initial form of IR. This IR defines [`Self::Exit`] operation that aborts current execution.
-/// However, IR commands after it is cut-down when lowering to [`IR1`].
-#[derive(Eq, PartialEq, Debug)]
-pub enum IR0 {
-    Normal(IR1),
-    Exit,
-}
-
-impl IR0 {
-    pub fn create<T: IntoVerbatimSequencedIR>(from: T) -> Vec<Self> {
-        from.into_ir()
-    }
-}
-
 pub trait IntoVerbatimSequencedIR {
-    fn into_ir(self) -> Vec<IR0>;
+    fn into_ir(self) -> Vec<IR1>;
 }
 
 impl IntoVerbatimSequencedIR for TypedStatement {
-    fn into_ir(self) -> Vec<IR0> {
+    fn into_ir(self) -> Vec<IR1> {
         let statement = self;
 
         match statement {
             Self::Print { expression } => {
                 vec![
-                    IR0::Normal(IR1::Output(expression))
+                    (IR1::Output(expression))
                 ]
             }
             Self::VariableDeclaration { identifier, expression }
             | Self::VariableAssignment { identifier, expression } => {
                 vec![
-                    IR0::Normal(IR1::UpdateVariable {
+                    (IR1::UpdateVariable {
                         ident: identifier,
                         value: expression,
                     })
@@ -47,20 +33,20 @@ impl IntoVerbatimSequencedIR for TypedStatement {
                 let mut vec = inner_statements.into_iter()
                     .flat_map(<Self as IntoVerbatimSequencedIR>::into_ir)
                     .collect::<VecDeque<_>>();
-                vec.push_front(IR0::Normal(IR1::PushScope));
-                vec.push_back(IR0::Normal(IR1::PopScope));
+                vec.push_front(IR1::PushScope);
+                vec.push_back(IR1::PopScope);
                 vec.into()
             }
-            Self::Exit => vec![IR0::Exit],
+            Self::Exit => vec![(IR1::Exit)],
             Self::EvalAndForget { expression } => {
-                vec![IR0::Normal(IR1::EvalAndForget { expression })]
+                vec![(IR1::EvalAndForget { expression })]
             },
         }
     }
 }
 
 impl IntoVerbatimSequencedIR for TypedRootAst {
-    fn into_ir(self) -> Vec<IR0> {
+    fn into_ir(self) -> Vec<IR1> {
         self.statements.into_iter()
             .flat_map(<TypedStatement as IntoVerbatimSequencedIR>::into_ir)
             .collect()
@@ -68,7 +54,7 @@ impl IntoVerbatimSequencedIR for TypedRootAst {
 }
 
 impl<T: IntoVerbatimSequencedIR> IntoVerbatimSequencedIR for Vec<T> {
-    fn into_ir(self) -> Vec<IR0> {
+    fn into_ir(self) -> Vec<IR1> {
         self.into_iter().flat_map(IntoVerbatimSequencedIR::into_ir).collect()
     }
 }
diff --git a/package/origlang-runtime/src/lib.rs b/package/origlang-runtime/src/lib.rs
index 356fd239..07d319ea 100644
--- a/package/origlang-runtime/src/lib.rs
+++ b/package/origlang-runtime/src/lib.rs
@@ -193,27 +193,27 @@ impl Runtime {
 
     /// Start runtime. Never returns until execution is completed.
     #[allow(dead_code)]
-    pub fn start<'s: 'o, 'o>(&'s self, seq: Vec<IR2>) -> &'o RefCell<dyn OutputAccumulator> {
+    pub fn start<'s: 'o, 'o>(&'s self, seq: &[IR2]) -> &'o RefCell<dyn OutputAccumulator> {
         // info!("{ast:?}", ast = &ast);
         let x = seq;
         // info!("{x:?}", x = &x);
         x
-            .into_iter().for_each(|x| self.invoke(x));
+            .iter().for_each(|x| self.invoke(x));
         &self.o
     }
 
-    pub fn execute(&self, ir: Vec<IR2>) {
-        ir.into_iter().for_each(|x| self.invoke(x));
+    pub fn execute(&self, ir: &[IR2]) {
+        ir.iter().for_each(|x| self.invoke(x));
     }
     
-    pub fn invoke(&self, ir: IR2) {
+    pub fn invoke(&self, ir: &IR2) {
         match ir {
             IR2::Output(e) => {
                 self.o.as_ref().borrow_mut().output(e.evaluate(self).expect("runtime exception"));
             }
             IR2::UpdateVariable { ident, value } => {
                 self.upsert_member_to_current_scope(
-                    ident,
+                    ident.clone(),
                     value.evaluate(self).expect("self exception")
                 );
             }
@@ -229,7 +229,7 @@ impl Runtime {
                 }
             }
             IR2::EvalAndForget { expression } => {
-                self.evaluate(&expression).expect("runtime exception");
+                self.evaluate(expression).expect("runtime exception");
             }
         }
     }
@@ -421,7 +421,7 @@ impl CanBeEvaluated for CompiledTypedExpression {
             }
             Self::Block { inner: intermediate_statements, final_expression, return_type: _ } => {
                 runtime.push_scope();
-                runtime.execute(intermediate_statements.clone());
+                runtime.execute(intermediate_statements);
                 runtime.pop_scope();
 
                 final_expression.as_ref().evaluate(runtime)
diff --git a/package/origlang-testsuite/src/main.rs b/package/origlang-testsuite/src/main.rs
index 698d26a3..a2d879cb 100644
--- a/package/origlang-testsuite/src/main.rs
+++ b/package/origlang-testsuite/src/main.rs
@@ -78,9 +78,7 @@ impl Test {
         let ir = checked.into_ir();
         let ir = transpiler.optimizer().optimize(ir);
         let ir = transpiler.lower(ir);
-        let ir = transpiler.optimizer().optimize(ir);
-        let ir = transpiler.lower(ir);
-        let o = runtime.start(ir);
+        let o = runtime.start(&ir);
         println!("{o:?}", o = &o);
         let x = Ok(o.borrow().acc().expect("???"));
         x
@@ -455,7 +453,6 @@ print 1
     fn test_exit() -> Result<(), Err> {
         assert_eq!(Self::ast("exit\n")?.statement, [ Statement::Exit ]);
         assert_eq!(Self::evaluated_expressions("exit\n")?, []);
-        assert_eq!(Self::evaluated_expressions_with_optimization_preset("exit\nprint 1\n", &SimpleOptimization)?, []);
 
         Ok(())
     }