Michael Fu
Ralph J. Tyser Professor of Management Science
Decision, Operations, and Information Technologies Department,
Robert H. Smith School of Business
joint appointment with the Institute for Systems Research
affiliate appointment with the Department of Electrical and Computer Engineering,
A. James Clark School of Engineering
offices: 4305 Van Munching Hall, 2229 A.V. Williams Building, (301) 405-2241
e-mail: mfu (at) umd (dot) edu
Highlights
- Co-Editor (with Saul I. Gass),
Encyclopedia of Operations Research and Management Science, 3rd edition, Springer, 2013 forthcoming.
-
National Science Foundation Operations Research Program Director: Sep.13, 2010 - Aug.24, 2012;
OR/MS Today articles about the Operations Research Program: part 1, part 2.
-
Distinguished Scholar-Teacher, 2004-2005
, University of Maryland.
- Fellow of INFORMS and IEEE.
- Guest Co-Editor (with Barry L. Nelson), Special Issue on Simulation Optimization,
ACM Transactions on Modeling and Computer Simulation, 2003.
- 2002
Institute for Systems Research Outstanding Faculty Award.
- 1999
IIE Operations Research Division Award.
- 1998
INFORMS
Simulation Society
OUTSTANDING SIMULATION PUBLICATION AWARD for the book,
Conditional Monte Carlo: Gradient Estimation and Optimization Applications
(co-author Jian-Qiang Hu).
- 1998
IIE Transactions on Operations Engineering Best Paper Award, for the paper,
Optimization of Discrete Event Systems via Simultaneous Perturbation Stochastic Approximation (co-author Stacy Hill).
Recent Invited Talks
- Stony Brook University, November 16, 2012.
- Rutgers Business School, September 10, 2012.
- Naval Postgraduate School, May 3, 2012.
- University of Washington, March 1, 2012.
- Arizona State University, December 9, 2011.
- Lehigh University, November 29, 2011.
- Macquarie University, Sydney, Australia, July 5, 2011.
- University of California at Berkeley, March 28, 2011.
- University of Illinois, March 14, 2011.
- University of Southampton, England, July 16, 2010.
- Peking University, June 30, 2010.
- Tsinghua University, Center for Intelligent & Networked Systems, July 2, 2010.
- United States Military Academy, West Point, NY, April 30, 2009.
- Zhejiang University, Hangzhou, China, July 23, 2009.
- University of Wisconsin, May 8, 2009.
- Duke University Fuqua School of Business, March 21, 2008.
- University of Minnesota, April 23, 2008.
Birthday Symposium/Conference Celebrations
EDUCATION
Math Genealogy Tree
Ph.D., Applied Mathematics, Harvard University, 1989; M.S., 1986;
National Science Foundation Graduate Fellow, 1995-98.
S.M., S.B., Electrical Engineering and Computer Science, S.B., Mathematics, MIT, 1985.
RESEARCH
Simulation modeling and analysis, production/inventory control, applied probability, and queueing theory;
stochastic derivative estimation, simulation optimization, Markov decision processes;
with application to supply chain management and financial engineering.
Current and Recent Research Projects
- Integrating Gradient and Adaptive Search in Simulation Optimization,
research sponsored by the National Science Foundation,
Project Director (co-PI Steve Marcus
and co-PI Jiaqiao Hu, SUNY Stony Brook), 2009-2013.
- Particle Filtering for Stochastic Control and Global Optimization,
research sponsored by the National Science Foundation,
co-Principal Investigator (PI Steve Marcus,
co-PI Enlu Zhou, University of Illinois), 2009-2012.
- Simulation-Based Methodologies for Global Optimization and Planning,
sponsored by the Air Force Office of Scientific Research,
co-Principal Investigator (PI Steve Marcus
and co-PI Jiaqiao Hu, SUNY Stony Brook), 2010-2013.
- Dynamic Real-Time Order Promising and Fulfillment for Global Make-to-Order Supply Chains,
sponsored by the National Science Foundation,
co-Principal Investigator (PI Michael Ball), 2006-2010.
- Simulation-Based Approaches to Solving Markov Decision Process,
research sponsored by the National Science Foundation,
Project Director (co-PI Steve Marcus), 2000-2007.
- Mathematical and Computational Finance Research Interactions Team (joint with Dilip Madan).
- Preventive Maintenance Scheduling in Semiconductor Manufacturing Fabs,
sponsored by the Semiconductor Research Corporation and International SEMATECH,
Project Director (with co-PI Steve Marcus and Emmanuel Fernandez, University of Cincinnati), 2001-2004.
Publications (click here for pdf file listing publications, including conference proceedings, book chapters, etc.)
BOOKS
- Conditional Monte Carlo: Gradient Estimation and Optimization Applications,
joint with J. Q. Hu; Kluwer Academic Publishers (now part of Springer), 1997 (order from Amazon.com).
Running list of errata. (Please e-mail any errors/typos you may catch. Thanks!)
- Perspectives in Operations Research: Papers in Honor of Saul Gass’ 80th Birthday, Springer, October 2006,
co-edited with Frank Alt and Bruce Golden (preface/TOC/photos, my article).
- Simulation-Based Methods for Markov Decision Processes
(with Hyeong Soo Chang, Jiaqiao Hu, Steve Marcus), Springer, March 2007 (preface/TOC).
- Advances in Mathematical Finance (Festschrift for Dilip Madan’s 60th birthday), Birkhäuser, July 2007,
co-edited with Robert Elliott, Bob Jarrow, and Ju-Yi Yen (preface/TOC/photos, my article) [also available at amazon.com]);
associated Conference (Sep.29-Oct.1, 2006).
Selected JOURNAL ARTICLES, Conference Proceedings, and Recent Working Papers
Markov decision processes
- An Adaptive Sampling Algorithm for Solving Markov Decision Processes, Operations Research, Vol.53, No.1, 126-139, 2005 (with H.S. Chang, J. Hu, S.I. Marcus) PDF
earlier version available as TR 2002-19.
- An Evolutionary Random Search Algorithm for Solving Markov Decision Processes, INFORMS Journal on Computing, Vol.19, No.2, 161-174, 2007 (with J. Hu, V. Ramezani, S.I. Marcus) PDF
earlier version available as TR 2005-3.
- Evolutionary Policy Iteration for Solving Markov Decision Processes, IEEE Transactions on Automatic Control, Vol.50, No.11, 1804-1808, 2005 (with H.S. Chang, H.-G. Lee, S.I. Marcus) PDF
earlier version available at TR 2002-31 (Note there is a minor technical error in one of the proofs in that version).
- Recursive Learning Automata Approach to Markov Decision Processes, IEEE Transactions on Automatic Control, Vol.52, No.7, 1249-55, 2007 (with H.S. Chang, J. Hu, S.I. Marcus). PDF
- A Two-Timescale Stochastic Approximation Algorithm for Weighted Cost-to-Go Markov Decision Processes, Proceedings of the 44th IEEE Conference on Decision and Control, 8022-8027, 2005 (with Y. He, S.I. Marcus). PDF
- An Asymptotically Efficient Algorithm for Finite Horizon Stochastic Dynamic Programming Problems, IEEE Transactions on Automatic Control, Vol.52, No.1, 89-94, 2007. PDF
earlier version available as TR 2003-26.
- TR 2005-84: Convergence of Sample Path Optimal Policies for Stochastic Dynamic Programming.
- TR 2003-25: A Distributed Algorithm for Solving a Class of Multi-agent Markov Decision Problems.
- TR 99-56: Simulation-Based Algorithms for Average Cost Markov Decision Processes.
randomized global optimization
- A Model Reference Adaptive Search Algorithm for Global Optimization, Operations Research, Vol.55, No.3, 549-568, 2007 (with J. Hu, S.I. Marcus). PDF
earlier version available as TR 2005-81.
- A Model Reference Adaptive Search Algorithm for Stochastic Global Optimization (with J. Hu, S.I. Marcus). PDF
- New Global Optimization Algorithms for Model-Based Clustering, under review (with J. Heath, W. Jank). PDF
- Global Convergence of Model Reference Adaptive Search for Gaussian Mixtures, under review (with J. Heath, W. Jank). PDF
- Model-Based Randomized Methods for Global Optimization, Proceedings of the 17th International Symposium on Mathematical Theory of Networks and Systems, 355-363, 2006 (with J. Hu, S.I. Marcus). PDF
gradient estimation (note: some papers also cross-listed under particular application area)
-
Naval Research Logistics
Cover Article, What You Should Know About Simulation and Derivatives, Vol.55, No.8, 723-736, 2008.
PDF
- Stochastic Gradient Estimation, Chapter 19, in Handbook on Operations Research and Management Science: Simulation, S.G. Henderson and B.L. Nelson, editors, Elsevier, 575-616, 2006. PDF
earlier version available as TR 2005-93.
- Extensions and Generalizations of Smoothed Perturbation Analysis in a Generalized Semi-Markov Process Framework, IEEE Transactions on Automatic Control, Vol.37, No.10, 1483-1500, 1992 (with J.Q.Hu). PDF
- Sample Path Derivatives for (s,S) Inventory Systems, Operations Research, Vol.42, No.2, 351-364, 1994. PDF
- Sensitivity Analysis for Simulation of Stochastic Activity Networks, in Perspectives in Operations Research: Papers in Honor of Saul Gass' 80th Birthday (eds. Alt, Fu, Golden), Springer, 351-366, 2006. PDF
- Simulation Optimization of Traffic Light Signal Timings via Perturbation Analysis, working paper (with W.C. Howell). PDF
- Online Traffic Light Control Through Gradient Estimation Using Stochastic Fluid Models, Proceedings of the IFAC 16th Triennial World Congress, 2005 (with C. Panayiotou, W.C. Howell). PDF
- Fluid Approximation and Perturbation Analysis of a Dynamic Priority Call Center, Proceedings of the 43rd IEEE Conference on Decision and Control, 2304-2309, 2004 (with M. Chen, J.Q. Hu). PDF
- Efficient Design and Sensitivity Analysis of Control Charts Using Monte Carlo Simulation, Management Science, Vol.45, No.3, 395-413, 1999 (with J.Q. Hu) PDF
earlier version available as TR 97-91.
- Conditional Monte Carlo Gradient Estimation in Economic Design of Control Charts, POM, under review. (with S. Lele, T. Vossen) PDF
- Second Derivative Sample Path Estimators for the GI/G/m Queue, Management Science, Vol.39, No.3, 359-383, 1993 (with J.Q.Hu). PDF
- Derivative Estimation for Buffer Capacity of Continuous Transfer Lines Subject to Operation-dependent Failures, Discrete Event Dynamic Systems, Vol.12, No.4, 447-469, 2002 (with X. Xie); PDF
earlier version available as TR 98-57.
- Efficient Sensitivity Analysis of Mortgage-Backed Securities (with J. Chen), unpublished manuscript, 2001. PDF
much abbreviated version available here (Hedging Beyond Duration and Convexity, Proceedings of the 2002 Winter Simulation Conference, 1593-1599).
- Sensitivity Analysis for Monte Carlo Simulation of Option Pricing, Probability in the Engineering and Information Sciences, Vol.9, No.3, 417-446, 1995 (with J.Q.Hu).
corrected version as pdf file (published version has some typos and errors).
- A Note on Perturbation Analysis Estimators for American-Style Options, Probability in Engineering and Informational Sciences, Vol.14, 385-392, 2000 (with R. Wu, G. Gürkan, A.Y. Demir). PDF
simulation optimization, stochastic approximation
- Optimization for Simulation: Theory vs. Practice (Feature Article), INFORMS Journal on Computing, Vol.14, No.3, 192-215, 2002. PDF
- Optimization via Simulation: A Review, Annals of Operations Research, Vol. 53, 199-248, 1994. PDF
- Two-Timescale Simultaneous Perturbation Stochastic Approximation Using Deterministic Perturbation Sequences, ACM Transactions on Modeling and Computer Simulation, 180-209, 2003 (with S. Bhatnagar, S.I. Marcus, I.J.Wang). PDF
- Convergence of Simultaneous Perturbation Stochastic Approximation for Nondifferentiable Optimization, IEEE Transactions on Automatic Control, Vol.48, No.8, 1459-1463, 2003 (with Y. He, S.I. Marcus). PDF
- On the Convergence Rate of Ordinal Comparison of Random Variables, IEEE Transactions on Automatic Control, Vol.,46, No.12, 1950-1954, 2001 (with X. Jin). PDF
- An Optimal Structured Feedback Policy for ABR Flow Control Using Two Timescale SPSA, IEEE/ACM Transactions on Networking, Vol.9, No.4, 479-491, 2001 (with S. Bhatnagar, S.I. Marcus, P.J.M. Fard); PDF
earlier version available as TR 99-86.
- Two Timescale Algorithms for Simulation Optimization of Hidden Markov Models, IIE Transactions, Vol.33, No.3, 245-258, 2001 (with S. Bhatnagar, S.I. Marcus, S. Bhatnagar); PDF
earlier version available as TR 2000-13.
- Optimization of Discrete Event Systems via Simultaneous Perturbation Stochastic Approximation, IIE Transactions, Vol. 29, No.3, pp.233-243, 1997 (with S.D. Hill). PDF
- Convergence of a Stochastic Approximation Algorithm for the GI/G/1 Queue Using Infinitesimal Perturbation Analysis, Journal of Optimization Theory and Applications, Vol.65, No.1, 149-160, 1990. PDF
simulation efficiency
- Simulation Allocation for Determining the Best Design in the Presence of Correlated Sampling, INFORMS Journal on Computing, Vol.19, No.1, 101-111, 2007 (with J.Q. Hu, C.H. Chen, X. Xiong). PDF
- Efficient Dynamic Simulation Allocation in Ordinal Optimization, IEEE Transactions on Automatic Control, Vol.51, No.12, 2005-2009, 2006 (with D. He, C.H. Chen). PDF
- Efficient Simulation Budget Allocation for Selecting an Optimal Subset, INFORMS Journal on Computing, under review (with D. He, C.H. Chen). PDF
- Asymptotically Optimal Simulation Allocation under Dependent Sampling, Mathematics of Operations Research, under review (with X. Xiong, S. Juneja). PDF
- Probabilistic Error Bounds for Simulation Quantile Estimation, Management Science, Vol.49, No.2, 230-246, 2003 (with X. Jin, X. Xiong); PDF
earlier version finalist in INFORMS Nicholson Student Paper competition: A Large Deviations Analysis of Quantile Estimation with Application to Value at Risk, available as pdf at DRUM.
financial engineering/computational finance
- Variance-Gamma and Monte Carlo, in Advances in Mathematical Finance (eds. Fu, Jarrow, Yen, Elliott), Birkhäuser, 21-35, 2007. PDF
(tutorial article on Monte Carlo simulation for Variance-Gamma process, including bridge sampling and sensitivity estimation)
- Pricing American-Style Derivatives with European Call Options, Management Science, Vol.52, No.1, 95-110, 2006 (with S. Laprise, S.I. Marcus, A.E.B. Lim, H. Zhang); PDF
much abbreviated preliminary version available here (A New Approach to Pricing American-Style Derivatives, Proceedings of the 2001 Winter Simulation Conference, 329-337).
- Optimal Exercise Policies and Simulation-based Valuation for American-Asian Options, Operations Research, Vol.51, No.1, 52-66, 2003 (with R. Wu). PDF
- Optimal Importance Sampling in Securities Pricing, Journal of Computational Finance, Vol.5, No.4, 27-50, 2002 (with Y. Su); PDF (Note: published version has numerous typos.)
much abbreviated preliminary version available here (Importance Sampling in Derivative Securities Pricing, Proceedings of the 2000 Winter Simulation Conference, 587-596).
- Pricing American Options: A Comparison of Monte Carlo Simulation Approaches, Journal of Computational Finance, Vol.4, No.3, 39-88, Spring 2001 (with S.B.Laprise, D.B. Madan, Y. Su, R. Wu). PDF
- Pricing Continuous Asian Options: A Comparison of Monte Carlo and Laplace Transform Inversion Methods, Journal of Computational Finance, Vol.2, No.2, 49-74, 1999 (with D.B. Madan, T. Wang). PDF
- Efficient Sensitivity Analysis of Mortgage-Backed Securities (with J. Chen), unpublished manuscript, 2001. PDF
much abbreviated version available here (Hedging Beyond Duration and Convexity, Proceedings of the 2002 Winter Simulation Conference, 1593-1599).
- Sensitivity Analysis for Monte Carlo Simulation of Option Pricing, Probability in the Engineering and Information Sciences, Vol.9, No.3, 417-446, 1995 (with J.Q.Hu).
corrected version as pdf file (published version has some typos and errors).
- A Note on Perturbation Analysis Estimators for American-Style Options, Probability in Engineering and Informational Sciences, Vol.14, 385-392, 2000 (with R. Wu, G. Gürkan, A.Y. Demir). PDF
semiconductor manufacturing and supply chain management
- Optimal Preventive Maintenance Scheduling in Semiconductor Manufacturing, IEEE Transactions on Semiconductor Manufacturing, Vol.17, No.3, 345-356, 2004 (with X. Yao, E. Fernández-Gaucherand, S.I. Marcus). PDF
- Optimal Joint Preventive Maintenance and Production Policies, Naval Research Logistics, Vol.52, No.7, 668-681, 2005 (with X. Yao, X. Xie, S.I. Marcus). PDF
- TR 2000-49: Approximate Policy Iteration for Semiconductor Fab-Level Decision Making - a Case Study
- TR 2000-48: Simulation-Based Approach for Semiconductor Fab-Level Decision Making - Implementation Issues
- TR 2000-1: Comparing Gradient Estimation Methods Applied to Stochastic Manufacturing Systems
queueing and inventory
- Optimization of (s,S) Inventory Systems with Random Lead Times and a Service Level Constraint, Management Science, Vol.44, No.12, S243-S256, 1998 (with S. Bashyam). PDF
- Queueing Theory in Manufacturing: A Review, Journal of Manufacturing Systems, Vol.18, No.3, 214-240, 1999 (with M.K. Govil). PDF
- Sample Path Derivatives for (s,S) Inventory Systems, Operations Research, Vol.42, No.2, 351-364, 1994. PDF
- Monotone Optimal Policies for a Transient Queueing Staffing Problem, Operations Research, No.2, 327-331, 2000 (with S.I. Marcus, I.J. Wang); PDF
earlier version available as TR 97-62.
- Minimizing Work-in-Process and Material Handling in the Facilities Layout Problem, IIE Transactions, Vol. 29, No.1, pp.29-36, 1997 (with B.K. Kaku); PDF
earlier version available as TR 95-41.
- Models for Multi-Echelon Repairable Item Inventory Systems with Limited Repair Capacity, European Journal of Operational Research, Vol. 97, No.3, pp.480-492, 1997 (with A. Diáz). PDF
- Second Derivative Sample Path Estimators for the GI/G/m Queue, Management Science, Vol.39, No.3, 359-383, 1993 (with J.Q.Hu). PDF
- TR 98-7: A Lower Bounding Result for the Optimal Policy in an Adaptive Staffing Problem.
- Multi-Echelon Models for Repairable Items: A Review (with A. Diaz). available as pdf at DRUM.
Note: other unpublished Technical Reports can be found at the ISR TR Web site.
TEACHING/MENTORING
Courses Taught
- BMGT 231 Statistical Models for Business
- BMGT 332 Operations Research for Management Decisions
- BMGT 435 Introduction to Applied Probability Models
- BMGT 671 Supply Chain Logistics and Operations Management (MBA Core Course Coordinator 1999-2005)
- BMGT 734 Models for Operations Management
- BMGT 772 Logistics Management (Executive MBA)
- BMGT 798B Computational Finance
- BMGT 798Z Operations Research in Finance
- BMGT 834 Operations Research: Probabilistic Models
- BMGT 835 Simulation of Discrete-Event Systems
PhD students current
- Huashuai Qu (co-advised with Ilya Ryzhov)
- Yijie Peng (visiting from Fudan University, Shanghai, China, advisor Prof. Jian-Qiang Hu)
- Marie Chau
- Liu Ming
- Crystal Oh (currently on leave)
PhD students graduated
1. Sridhar Bashyam, currently at Frito Lay.
2.
Angel Díaz, currently on faculty at Instituto de Empresa, Madrid, Spain.
3. Jae-sin Yoo (co-advisor Arjang Assad).
4.
Kefeng Xu (co-advisor Phil Evers), currently on faculty at University of Texas–San Antonio.
5. Tong Wang (co-advisor Dilip Madan), currently at the World Bank.
6. Yi Su (co-advisor Dilip Madan).
7. Rongwen Wu (co-advisor Dilip Madan), currently senior director at Capitol One (previously Freddie Mac).
8. Xing Jin (co-advisor Dilip Madan), currently on faculty at Warwick Business School (previously in math department at National University of Singapore).
9. Scott Laprise, currently at BAE Systems.
10. Ying He (co-advisor Steve Marcus), currently at Fannie Mae (previously NIH, IMF).
11. Xiaodong Yao (co-advisor Steve Marcus), currently at SAS.
12. Jian Chen, currently at
(previously at Fannie Mae, Freddie Mac).
13. Ahmad Ridley (co-advisor Bill Massey), currently at MitreTek.
14. Xiaoping Xiong, currently at Freddie Mac.
15. Sun-Hee Kim (co-advisor Dilip Madan).
16. Jiaqiao Hu (co-advisor Steve Marcus), currently on Applied Mathematics & Statistics faculty at SUNY Stony Brook.
17. William Howell, previously at BAE Systems.
18. Huiju Zhang, currently VP at Morgan Stanley (previously Fitch Ratings, Capital One).
19. Jeff Heath (co-advisor Wolfgang Jank), currently on faculty at Centre College.
20. Colonel Scott Nestler (co-advisor Dilip Madan), currently at U.S. Army War College (previously on faculty of U.S. Military Academy at West Point, Naval Postgraduate School).
21. Lt. Colonel Andrew Hall, currently on The Joint Staff at the Pentagon (previously on faculty of U.S. Military Academy at West Point).
22. Enlu Zhou (co-advisor Steve Marcus), currently on faculty of University of Illinois.
23. Matthew Reindorp,
currently on faculty of Technical University of Eindhoven.
24. Lingyan Cao (co-advisor Dilip Madan),
currently at IMF.
25. Yongqiang Wang (co-advisor Steve Marcus),
currently at Campbell and Company.
Postdoctoral Fellows supervised (all jointly with Steve Marcus)
- Shalabh Bhatnatar, 1997-2000, currently on faculty at Indian Institute for Science, Bangalore.
- Andrew Lim, 2001, currently on faculty at University of California, Berkeley.
- Grazyna Badowski, 2001-2002.
- Vijay Konda, 2002-2003.
- Vahid Ramezani, 2003-2005.
- Chang Su, 2004-2005.
PROFESSIONAL ACTIVITIES
- Program Chair, 2011 Winter Simulation Conference (December 11-14, Phoenix, AZ).
- Stochastic Models and Simulation Department Editor, Management Science, 2006-2008.
- Associate Editor, Mathematics of Operations Research, 2006-2008.
- Simulation Area Editor, Operations Research, 2000-2005 (Associate Editor, 1998-99).
- Associate Editor, Management Science, 1998-2005.
- Associate Editor, INFORMS Journal on Computing, 1993-2000.
- Associate Editor, IIE Transactions, 1994-2000.
- Editorial Board, Production and Operations Management, 1996-2003.
- Fellow of INFORMS (formerly ORSA, TIMS)
and IEEE.
- Member of Program Committee, 2013 INFORMS Applied Probability Society Meeting.
- Member of Program Committee, 2011 INFORMS Computing Society Conference.
- Member of Organizing/Program Committee, 2008 MSOM Meeting.
- Member of Program Committee, 46th IEEE Conference on Decision and Control, 2007.
- Member of Organizing Committee, Mathematical Finance Conference in honor of Dilip Madan on his 60th birthday, 2006.
- Chair of Organizing Committee, Operations Research Symposium in honor of Saul Gass on his 80th birthday, 2006.
- Member of Program Committee, 2004 INFORMS Applied Probability Society Meeting.
- Member of Program Committee, 2000 INFORMS Computing Society Conference.
- Member of Program Committee, 1998 INFORMS Computer Science Technical Section Conference.
- Member of Program Committee, in charge of Contributed Papers, 1996 INFORMS Spring National Meeting.
- Member of Scientific Committee, 1995 International Conference on Emerging Technologies and Factory Automation.
Resources
Favorite Quotes
-
"Give a man a fish, feed him for a day; teach him how to fish, feed him for a lifetime." –Lao Tzu (Lao Tse, Laozi)
- “Chance favors the prepared mind.” –Louis Pasteur
- "When life hands you a lemon, make lemonade."
- “It is not possible to wait for inspiration, and even inspiration alone is not sufficient. Work and more work is necessary.
Man blessed by genius can create nothing really great, not even anything mediocre, if he does not toil as hard as a slave.” –Peter Ilyich Tchaikovsky
- “As a well spent day brings happy sleep, so a life well used brings happy death.” -Leonardo da Vinci