Soohan Lim

Curriculum Vitae

Integrated MS/PhD Candidate in Computer Science, Yonsei University
Research on LLM-based Program Reliability and Efficiency Enhancement

Profile

My research focuses on enhancing the reliability and efficiency of programs with LLMs. Efficiency concerns how much computation a program needs and where its bottlenecks arise; beyond predicting complexity, I generate inputs that expose real bottlenecks so inefficiency can be verified through execution. Reliability concerns whether generated code satisfies not only the required functionality but also its input contracts; I build benchmarks that quantify this and design generation methods that raise specification satisfaction. Neither problem can be judged from the final output alone, so I take a neuro-symbolic approach in which LLMs interpret natural language while structuring and verification are delegated to deterministic rules, constraint solvers, and actual execution. I have carried out five studies around these problems, four as first author including equal contributions, moving from cost prediction (TCProF, MEC³O) to bottleneck-exposing tests (STAB), and from functional-correctness evaluation to specification-compliance evaluation (ContractEval) and improvement (SLICE). Most recently I extended the same execution-aware view to provenance: SEW watermarks already generated code through keyed code-style choices and detects them with calibrated, context-aware evidence.

Education

Experience

Theory of Computation Lab, Yonsei University

Publications

Click an entry to see my role, the period, and a short summary.

arXiv
SEW: Style-Encoded Watermarking of LLM-Generated Code Soohan Lim, Hyundong Jin, Yo-Sub Han† arXiv Preprint 2026

First author2026.07 – 2026.09

Task
Embedding and detecting a watermark in already generated code for provenance tracking, without hurting functional correctness and without false detections on human-written code.
Method
Code style rules collected from style guides and transformation rules are applied with style choices fixed by a secret key and each program's structural context. Detection calibrates watermark evidence with style probabilities estimated from human-written code and aggregates evidence across structurally matching locations so repeated choices cannot inflate it.
Tech
Style-rule transformations, keyed style selection, style-preference calibration, context-aware evidence aggregation; CodeContests across three LLMs and three languages
arXiv
SLICE: Specification-Level Isolation of Contract Enforcement Soohan Lim, Hyundong Jin, Yo-Sub Han† arXiv Preprint 2026

First author2026.05 – 2026.07

Task
Generating code from a natural-language specification that satisfies both the functional requirements and the input contracts.
Method
The specification is structured as a graph to separate functional requirements from contract conditions. Candidate bodies from the functional view are ranked by executing specification examples; contract assertions are generated separately, screened by execution, and merged into the selected body.
Tech
Specification graph, multi-candidate LLM generation, execution-based verification, token log-probability selection
arXiv
STAB: Specification-driven Testing for Algorithmic Bottlenecks Soohan Lim*, Joonghyuk Hahn*, Hyundong Jin, Yo-Sub Han† arXiv Preprint 2026

Co-first author2026.02 – 2026.05

Task
Generating test inputs that trigger an algorithm's worst-case execution path from the natural-language specification alone, without a reference implementation.
Method
A Constraint Saturator computes the largest admissible input size from the variable relations and range constraints, and an Adversarial Scenario Injector injects input structures from 13 bottleneck scenarios.
Tech
LLM constraint interpretation, CP-SAT constraint optimization, isolated DOMjudge · Docker execution
ACL 2026
ContractEval: A Benchmark for Evaluating Contract-Satisfying Assertions in Code Generation Soohan Lim*, Joonghyuk Hahn*, Hyunwoo Park, Sang-Ki Ko, Yo-Sub Han† Findings of ACL 2026

Co-first author2025.09 – 2026.02

Task
Building a benchmark that tests whether generated code actually checks its input contracts (type, range, and structure constraints).
Method
An LLM translates reference assertions into SMT-LIB constraints, an SMT solver finds inputs that violate exactly one targeted contract, and reference-code execution keeps only tests that trigger the intended violation, yielding 364 tasks.
Tech
Neuro-symbolic pipeline (LLM + Z3), HumanEval+/MBPP+, execution-based test filtering
KCC 2026
K-SpecDetox: Korean Spectral Energy-based Detection and Detoxification of Dialect Profanity Soohan Lim, Sang-Min Choi, Yo-Sub Han KCC 2026 (Poster)

First author2026.01 – 2026.05

Task
Detecting profanity in Korean dialect sentences, quantifying its toxicity, and generating detoxified sentences that keep the dialect endings.
Method
Token log-probabilities are treated as a signal; FFT spectral energy and a sampling-discrepancy score feed an SVM detector. Toxicity is graded into three levels, level-specific prompts produce the detoxified sentence, and a spectral re-verification loop regenerates weak outputs.
Tech
FFT spectral analysis, SVM, dictionary-based pre-processing, LLM prompting
arXiv
MEC³O: Multi-Expert Consensus for Code Time Complexity Prediction Joonghyuk Hahn*, Soohan Lim*, Yo-Sub Han† arXiv Preprint 2025

Co-first author2024.12 – 2025.02

Task
Predicting the time-complexity class of source code (O(1) to O(2n)).
Method
The best-performing LLM per complexity class is assigned as its expert with a class-specific instruction; experts exchange feedback in a structured debate, and a weighted consensus of expertise and confidence makes the final decision.
Tech
Multi-agent debate, expert role prompting, weighted consensus algorithm
KCC 2025
K-ToPiC: Korean Dialect Toxicity Polishing with Curriculum Learning-based Span Detection Jungin Kim*, Soohan Lim*, Hyeseon Ahn, Sang-Min Choi, Yo-Sub Han† KCC 2025 (Oral Presentation)

Co-first author2025.03 – 2025.07

Task
Detecting profanity spans in Korean dialect sentences and polishing only those spans while preserving the dialect style.
Method
A 30,457-pair standard-to-dialect dictionary applied to KOLD yields a 28,435-sentence dialect profanity dataset; span detection is trained with a span-length curriculum, and the detected span plus a masked sentence guide the LLM to soften only the necessary expressions.
Tech
Curriculum learning, LLM fine-tuning (polyglot-ko, kullm-polyglot), detoxification generation (gemma, Bllossom)
NAACL 2025
TCProF: Time-Complexity Prediction SSL Framework Joonghyuk Hahn, Hyeseon Ahn, Jungin Kim, Soohan Lim, Yo-Sub Han† NAACL 2025 (Oral Presentation)

Co-author2024.02 – 2024.12

Task
Predicting the time complexity of code in a low-resource setting with few labeled examples.
Method
Code augmentation (loop conversion, back-translation) and a symbolic module enrich the features, and two models trained on original and augmented data exchange pseudo-labels through co-training. I handled the baseline experiments and the co-training implementation.
Tech
Semi-supervised learning (co-training), AST · regex symbolic analysis, code augmentation
KSC 2024
CA-DiaL: Curriculum and Attribute-Based Learning for Korean Dialect Translation using LLMs Soohan Lim, Joonghyuk Hahn, Hyeseon Ahn, Sang-Min Choi, Yo-Sub Han† KSC 2024 (Poster)

First author2024.08 – 2024.09

Task
Training an LLM translator that converts Gyeongsang dialect sentences into standard Korean.
Method
Training data are split into three curriculum levels by the number of dialect words per sentence, and speaker gender and age-group attributes are prepended as a header so the model learns easy sentences and speaker patterns first.
Tech
QLoRA fine-tuning (Solar, KoAlpaca-Polyglot, Korean-Bllossom), AI-Hub dialect corpus

* co-first authorship; † corresponding author. See the Publications page for links and BibTeX.

Skills

Advisor

Prof. Yo-Sub Han
Department of Computer Science, Yonsei University
Email: emmous@yonsei.ac.kr

Last updated: October 2026