diff --git a/offchain/Cargo.toml b/offchain/Cargo.toml
index 62a6f91..561dd5a 100644
--- a/offchain/Cargo.toml
+++ b/offchain/Cargo.toml
@@ -15,6 +15,10 @@ path = "src/bin/gp_spec_tester.rs"
 name = "symreg_experiment"
 path = "src/bin/symreg_experiment.rs"
 
+[[bin]]
+name = "symreg_experiment_local"
+path = "src/bin/symreg_experiment_local.rs"
+
 [dependencies]
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
diff --git a/offchain/src/bin/symreg_experiment.rs b/offchain/src/bin/symreg_experiment.rs
index dd57de5..1c7e1b9 100644
--- a/offchain/src/bin/symreg_experiment.rs
+++ b/offchain/src/bin/symreg_experiment.rs
@@ -64,7 +64,7 @@ fn evaluate_ast_on_x(
 
     // e) If final_int_stack is empty => 0, else top item
     if outputs.final_int_stack.is_empty() {
-        0
+        i32::MAX
     } else {
         *outputs.final_int_stack.last().unwrap() as i32
     }
@@ -77,14 +77,22 @@ fn evaluate_fitness(
     samples: &[(i32, i32)]
 ) -> f64 {
     let mut error_sum = 0.0;
-    for &(x, target_y) in samples {
-        let predicted = evaluate_ast_on_x(runner, ast, x);
-        let diff = (predicted - target_y) as f64;
-        error_sum += diff * diff;
+    for &(x, target_y32) in samples {
+        // cast to i64
+        let target_y = target_y32 as i64;
+        
+        // evaluate in i64 as well
+        let predicted_i64 = evaluate_ast_on_x(runner, ast, x) as i64;
+        
+        let diff = predicted_i64.wrapping_sub(target_y); 
+        // or you could saturating_sub if you prefer
+
+        error_sum += (diff as f64) * (diff as f64);
     }
     error_sum / samples.len() as f64
 }
 
+
 fn main() -> Result<()> {
     // 1) Generate samples for f(x)=3x^2 + x + 3
     let samples = generate_samples();
@@ -95,10 +103,10 @@ fn main() -> Result<()> {
     let mut runner = EvmRunner::new(creation_bytes)?;
 
     // 3) GP parameters
-    let pop_size = 1000;  // must be divisible by 4 for our scheme
-    let generations = 30;
+    let pop_size = 4000;  // must be divisible by 4 for our scheme
+    let generations = 100;
     let early_stop_threshold = 1.0;
-    let max_points = 15;
+    let max_points = 20;
 
     assert_eq!(pop_size % 4, 0, "pop_size must be multiple of 4 for our scheme");
     let quarter = pop_size / 4;
@@ -129,15 +137,15 @@ fn main() -> Result<()> {
         println!("Best error = {best_err}");
 
         // Print top 5 subjects in pretty format
-        let top_n = 5.min(scored.len());
-        println!("Top {top_n} subjects:");
-        for i in 0..top_n {
-            println!(
-                "  #{i}, err={}, AST:\n{:#?}",
-                scored[i].1,
-                scored[i].0
-            );
-        }
+        // let top_n = 5.min(scored.len());
+        // println!("Top {top_n} subjects:");
+        // for i in 0..top_n {
+        //     println!(
+        //         "  #{i}, err={}, AST:\n{:#?}",
+        //         scored[i].1,
+        //         scored[i].0
+        //     );
+        // }
 
         // early stop?
         if best_err < early_stop_threshold {
@@ -186,12 +194,30 @@ fn main() -> Result<()> {
         population = new_pop;
     }
 
-    // 6) Final population => we can evaluate & print
-    println!("\n=== Final Population ===");
-    for (i, ast) in population.iter().enumerate() {
-        let err = evaluate_fitness(&mut runner, ast, &samples);
-        println!("Subject #{i}, err={err}, AST:\n{:#?}", ast);
-    }
+    // 6) Final population => evaluate & sort, then print only top 10
+    println!("\n=== Final Population (Top 10) ===");
 
+    // a) Evaluate each item in the final population
+    let mut final_scored: Vec<(UntypedAst, f64)> = population
+        .into_iter()
+        .map(|ast| {
+            let err = evaluate_fitness(&mut runner, &ast, &samples);
+            (ast, err)
+        })
+        .collect();
+    
+    // b) Sort ascending by error
+    final_scored.sort_by(|a, b| a.1.partial_cmp(&b.1).unwrap());
+    
+    // c) Print the top 10 (or fewer if the population is smaller)
+    let top_n = 10.min(final_scored.len());
+    for i in 0..top_n {
+        let (ref ast, err) = final_scored[i];
+        println!(
+            "Subject #{i}, err={err}, AST:\n{:#?}",
+            ast
+        );
+    }
+    
     Ok(())
 }
diff --git a/offchain/src/bin/symreg_experiment_local.rs b/offchain/src/bin/symreg_experiment_local.rs
new file mode 100644
index 0000000..58df871
--- /dev/null
+++ b/offchain/src/bin/symreg_experiment_local.rs
@@ -0,0 +1,202 @@
+// src/bin/symreg_experiment_local.rs
+
+use anyhow::Result;
+use rand::{thread_rng, Rng};
+
+// Our GP + compiler modules (adjust paths if needed)
+use offchain::compiler::ast::{UntypedAst, Push3Ast};
+use offchain::helpers::artifact::get_creation_code;
+use offchain::runner::revm_runner::{EvmRunner, Push3InterpreterInputs};
+use offchain::compiler::push3_describtor::make_sublist_descriptor;
+
+// Our random code and local mutation
+use offchain::gp::generate_spec::ranmdom_code_fixed;
+use offchain::gp::local_mutation::local_mutation_fixed;
+
+// Ethers + ABI
+use ethers::types::U256;
+use ethers::abi::{encode, Token};
+
+/// 1) Generate (x, y) samples for f(x) = 3x^2 + x + 3
+fn generate_samples() -> Vec<(i32, i32)> {
+    let mut samples = Vec::new();
+    for x in -5..=5 {
+        let y = 3 * x * x + x + 3;
+        samples.push((x, y));
+    }
+    samples
+}
+
+/// 2) Evaluate a single AST on a single input `x`, returning the final top of the int stack.
+fn evaluate_ast_on_x(
+    runner: &mut EvmRunner,
+    ast: &UntypedAst,
+    x: i32,
+) -> i32 {
+    // Convert AST => push3 bytecode
+    let code_bytes = ast.to_bytecode();
+    let code_len = code_bytes.len() as u32;
+
+    // Build a sublist descriptor
+    let descriptor = make_sublist_descriptor(0, code_len);
+
+    // Provide x in `init_int_stack`
+    let inputs = Push3InterpreterInputs {
+        code: code_bytes,
+        init_code_stack: Vec::new(),
+        init_exec_stack: vec![descriptor],
+        init_int_stack: vec![x as i128],
+    };
+
+    // Run
+    let outputs = match runner.run_interpreter(&inputs) {
+        Ok(o) => o,
+        Err(_) => {
+            // If revert => 0
+            return 0;
+        }
+    };
+
+    if outputs.final_int_stack.is_empty() {
+        i32::MAX  // or 0, or i32::MAX to strongly penalize weird runs
+    } else {
+        *outputs.final_int_stack.last().unwrap() as i32
+    }
+}
+
+/// 3) Evaluate an AST on all samples => compute MSE
+fn evaluate_fitness(
+    runner: &mut EvmRunner,
+    ast: &UntypedAst,
+    samples: &[(i32, i32)]
+) -> f64 {
+    let mut error_sum = 0.0;
+    for &(x, target_y32) in samples {
+        // cast to i64
+        let target_y = target_y32 as i64;
+        
+        // evaluate in i64
+        let predicted_i64 = evaluate_ast_on_x(runner, ast, x) as i64;
+        
+        // wrapping_sub to avoid panic
+        let diff = predicted_i64.wrapping_sub(target_y);
+        error_sum += (diff as f64) * (diff as f64);
+    }
+    error_sum / samples.len() as f64
+}
+
+fn main() -> Result<()> {
+    // 1) Generate samples
+    let samples = generate_samples();
+
+    // 2) Setup ephemeral EVM runner
+    let creation_hex_filename = "../onchain/out/Push3Interpreter.sol/Push3Interpreter.json";
+    let creation_bytes = get_creation_code(creation_hex_filename)?;
+    let mut runner = EvmRunner::new(creation_bytes)?;
+
+    // 3) GP parameters
+    let pop_size = 3600;  // must be multiple of 3 for our scheme
+    let generations = 100;
+    let early_stop_threshold = 1.0;
+    let max_points = 12;  // random code size limit
+
+    // Ensure pop_size is multiple of 3
+    assert_eq!(pop_size % 3, 0, "pop_size must be multiple of 3 for our scheme");
+    let third = pop_size / 3;
+
+    let mut rng = thread_rng();
+
+    // 4) Initialize random population
+    let mut population: Vec<UntypedAst> = (0..pop_size)
+        .map(|_| ranmdom_code_fixed(&mut rng, max_points))
+        .collect();
+
+    // 5) Main loop
+    for gen in 0..generations {
+        // a) Evaluate
+        let mut scored: Vec<(UntypedAst, f64)> = population.into_iter()
+            .map(|ast| {
+                let err = evaluate_fitness(&mut runner, &ast, &samples);
+                (ast, err)
+            })
+            .collect();
+        
+        // b) Sort ascending by error
+        scored.sort_by(|a, b| a.1.partial_cmp(&b.1).unwrap());
+
+        let best_err = scored[0].1;
+        println!("\n=== Generation {gen} ===");
+        println!("Best error = {best_err}");
+
+        // (Optionally) Print top 5 in pretty format
+        let top_n = 5.min(scored.len());
+        println!("Top {top_n} subjects:");
+        for i in 0..top_n {
+            println!(
+                "  #{i}, err={}, AST:\n{:#?}",
+                scored[i].1, 
+                scored[i].0
+            );
+        }
+
+        // check early stop
+        if best_err < early_stop_threshold {
+            println!("Best error < {early_stop_threshold}, stopping early!");
+            population = scored.into_iter().map(|(a, _)| a).collect();
+            break;
+        }
+
+        // c) Build new population:
+        //   - 1/3 = best survivors
+        //   - 1/3 = fresh random
+        //   - 1/3 = local mutation
+        let mut new_pop = Vec::with_capacity(pop_size);
+
+        // keep best third
+        for i in 0..third {
+            new_pop.push(scored[i].0.clone());
+        }
+
+        // random third
+        for _ in 0..third {
+            let fresh = ranmdom_code_fixed(&mut rng, max_points);
+            new_pop.push(fresh);
+        }
+
+        // local mutation third
+        let top_half_count = scored.len() / 2; 
+        // we'll pick parents from top half for local mutation
+        while new_pop.len() < pop_size {
+            let idx = rng.gen_range(0..top_half_count);
+            // we assume you have local_mutation_fixed
+            // if you prefer passing a custom InstructionSet, do local_mutation(..., &instr_set)
+            let mutated = offchain::gp::local_mutation::local_mutation_fixed(
+                &scored[idx].0,
+                &mut rng
+            );
+            new_pop.push(mutated);
+        }
+
+        // store for next generation
+        population = new_pop;
+    }
+
+    // 6) Final => evaluate & sort => top 10
+    println!("\n=== Final Population (Top 10) ===");
+    let mut final_scored: Vec<(UntypedAst, f64)> = population
+        .into_iter()
+        .map(|ast| {
+            let err = evaluate_fitness(&mut runner, &ast, &samples);
+            (ast, err)
+        })
+        .collect();
+    final_scored.sort_by(|a, b| a.1.partial_cmp(&b.1).unwrap());
+
+    let top_n = 10.min(final_scored.len());
+    for i in 0..top_n {
+        let (ref ast, err) = final_scored[i];
+        println!("Subject #{i}, err={err}, AST:\n{:#?}", ast);
+    }
+
+    Ok(())
+}
diff --git a/offchain/src/gp/generate_spec.rs b/offchain/src/gp/generate_spec.rs
index 3004403..0ac4976 100644
--- a/offchain/src/gp/generate_spec.rs
+++ b/offchain/src/gp/generate_spec.rs
@@ -47,7 +47,7 @@ impl InstructionSet {
             InstructionAtom::Opcode(op) => UntypedAst::Instruction(op.clone()),
             InstructionAtom::EphemeralInt => {
                 // For ephemeral int, produce a random literal in some range
-                let val = rng.gen_range(-100..100);
+                let val = rng.gen_range(-30..30);
                 UntypedAst::IntLiteral(val)
             }
         }
diff --git a/offchain/src/gp/local_mutation.rs b/offchain/src/gp/local_mutation.rs
new file mode 100644
index 0000000..5170924
--- /dev/null
+++ b/offchain/src/gp/local_mutation.rs
@@ -0,0 +1,114 @@
+//! src/gp/local_mutation.rs
+//! A localized mutation operator that makes small tweaks depending on node type.
+
+use rand::Rng;
+use crate::compiler::ast::{UntypedAst, OpCode};
+use crate::gp::mutation::{
+    enum_nodes_dfs, get_subtree, replace_subtree,
+};
+use crate::gp::generate_spec::{
+    InstructionAtom, InstructionSet,
+};
+
+/// A top-level function to perform a localized mutation with a chosen `InstructionSet`.
+pub fn local_mutation(
+    original: &UntypedAst,
+    rng: &mut impl Rng,
+    instr_set: &InstructionSet,
+) -> UntypedAst {
+    let all_paths = enum_nodes_dfs(original);
+    let idx = rng.gen_range(0..all_paths.len());
+    let chosen_path = &all_paths[idx];
+
+    let old_subtree = get_subtree(original, chosen_path);
+    let new_subtree = local_mutation_node(&old_subtree, rng, instr_set);
+    replace_subtree(original, chosen_path, new_subtree)
+}
+
+/// A convenience wrapper that always uses `InstructionSet::new_default()`.
+pub fn local_mutation_fixed(
+    original: &UntypedAst,
+    rng: &mut impl Rng,
+) -> UntypedAst {
+    let instr_set = InstructionSet::new_default();
+    local_mutation(original, rng, &instr_set)
+}
+
+fn local_mutation_node(
+    subtree: &UntypedAst,
+    rng: &mut impl Rng,
+    instr_set: &InstructionSet,
+) -> UntypedAst {
+    match subtree {
+        UntypedAst::IntLiteral(val) => {
+            let delta = rng.gen_range(-5..=5);
+            let new_val = val.saturating_add(delta);
+            UntypedAst::IntLiteral(new_val)
+        }
+        UntypedAst::Instruction(op) => {
+            let mut new_op = pick_random_opcode(rng, instr_set);
+            for _ in 0..3 {
+                if &new_op != op {
+                    break;
+                }
+                new_op = pick_random_opcode(rng, instr_set);
+            }
+            UntypedAst::Instruction(new_op)
+        }
+        UntypedAst::Sublist(children) => {
+            let choice = rng.gen_range(0..3);
+            let mut new_children = children.clone();
+
+            match choice {
+                0 => {
+                    // remove one child if possible
+                    if !new_children.is_empty() {
+                        let i = rng.gen_range(0..new_children.len());
+                        new_children.remove(i);
+                    }
+                }
+                1 => {
+                    // insert a new small node
+                    let i = rng.gen_range(0..=new_children.len());
+                    let node = create_small_node(rng, instr_set);
+                    new_children.insert(i, node);
+                }
+                2 => {
+                    // reorder two children
+                    if new_children.len() > 1 {
+                        let i = rng.gen_range(0..new_children.len());
+                        let j = rng.gen_range(0..new_children.len());
+                        new_children.swap(i, j);
+                    }
+                }
+                _ => {}
+            }
+
+            UntypedAst::Sublist(new_children)
+        }
+    }
+}
+
+fn pick_random_opcode(rng: &mut impl Rng, instr_set: &InstructionSet) -> OpCode {
+    use crate::compiler::ast::OpCode;
+
+    let mut opcode_list: Vec<&OpCode> = Vec::new();
+    for atom in &instr_set.atoms {
+        if let InstructionAtom::Opcode(ref op) = atom {
+            opcode_list.push(op);
+        }
+    }
+    if opcode_list.is_empty() {
+        // fallback => default to Noop
+        return OpCode::Noop;
+    }
+    let i = rng.gen_range(0..opcode_list.len());
+    opcode_list[i].clone()
+}
+
+fn create_small_node(
+    rng: &mut impl Rng,
+    instr_set: &InstructionSet,
+) -> UntypedAst {
+    instr_set.random_atom_as_ast(rng)
+}
diff --git a/offchain/src/gp/mod.rs b/offchain/src/gp/mod.rs
index 3b107c3..91c726c 100644
--- a/offchain/src/gp/mod.rs
+++ b/offchain/src/gp/mod.rs
@@ -3,3 +3,4 @@ pub mod genetic_ops;
 pub mod generate;
 pub mod generate_spec;
 pub mod mutation;
+pub mod local_mutation;