Tierra Tutorial

Tom Ray - ATR, OU
Joseph Hart - ATR

• This presentation: http://www.hip.atr.co.jp/~ray/pubs/pubs.html http://www.hip.atr.co.jp/~ray/pubs/tutorial/Tutorial.ppt
• Tierra Home Page: http://www.hip.atr.co.jp/~ray/tierra/tierra.html
• Tom Ray: tray@ou.edu http://www.hip.atr.co.jp/~ray/
• Joseph Hart: jhart@hip.atr.co.jp http://www.hip.atr.co.jp/~jhart/

• Concept - Motivation
• The Virtual Machine
• Using Tierra
• Tools
• The Ancestor
• Results
• Network Tierra
• Future Directions

• Concept - Motivation
• The Virtual Machine
• Using Tierra
• Tools
• The Ancestor
• Results
• Network Tierra
• Future Directions

• Biological - original motivations
• Computational - later motivations

• Biological - original motivations
• Computational - later motivations

• Life on Earth is a single instance of evolution (sample size of one)
• Create and observe a new and independent instance of evolution
• Broaden our perspective of evolution (and therefore of life) by increasing the sample size (to more than one)
• Observe the properties of evolution in a new and radically different medium (digital rather than organic)

• Evolution by natural selection on Earth has organized the form and process of matter and energy from the molecular level up through the ecosystem level

• The organization generated by evolution spans about twelve orders of magnitude of scale
• from the molecular to the ecosystem level

• At each level of scale, there are richly organized structures and processes

• At each level of scale, the structures are built hierarchically from the structures of the level below

• All of this rich hierarchically organized structure through twelve orders of magnitude of scale,
• was built by the process of evolution by natural selection embedded in the medium of carbon chemistry.

• Life on Earth is the product of evolution by natural selection operating in the medium of carbon chemistry.
• However, in theory, the process of evolution is neither limited to occurring on the Earth, nor in carbon chemistry.
• Just as it may occur on other planets, it may also operate in other media, such as the medium of digital computation.
• And just as evolution on other planets is not a model of life on Earth, nor is natural evolution in the digital medium.

• The digital medium is not a material medium.
• It is a logical, informational medium.
• The digital medium does not exhibit the laws of thermodynamics.
• Cyberspace is not a 3D Euclidean space.
• We are not constrained by the same laws of physics, unless we impose them upon ourselves.

• Evolutions sees the medium that it is embedded in.
• In the organic medium, evolutions sees the laws of conventional chemistry and physics.
• In the digital medium, evolution sees the logic of the machine code, the rules of the operating system, and the structure of memory,
• as a surrogate physics and chemistry.

• Embedded within the digital medium, evolution can not see the hardware from which the computer is constructed.
• Mechanical switches, vacuum tubes, transistors, integrated circuits,
• all look the same to evolution if they implement the same logic.
• Evolution only sees the logic.

• A computer built from integrated circuits will be faster than one built from mechanical switches.
• But the unit of time is the CPU clock cycle.
• From within the digital medium, evolution can not tell if it is a second or a nanosecond

• Cyberspace is not a Euclidean space.
• There is no obvious distance metric.
• How can we analyze the topology?

• The time that it takes to move data between two points might serve as a distance metric.
• Within the (flat) RAM memory of a single computer, all pairs of points are equidistant.
• Points in cache memory are closer together.
• Points on disk memory are farther apart.
• Distances between machines depend on network topology and traffic conditions.

• Biological - original motivations
• Computational - later motivations

• Digital evolution produced dramatic optimizations of machine code
• Evolution might be used to:
• Optimize useful software
• Create new software
• Create software of greater complexity than human programmers can write
• Find the true nature of the digital medium by "becoming one" with it, the Zen of digital life

• We are all robots
• Our bodies are made of metal and our brains of silicon chips
• We have no experience or knowledge of carbon based life,
• not even in our science fiction

• Now one of us robots comes to our academic gathering with a flask of methane, ammonia, hydrogen, water, and some dissolved minerals.
• The robot asks: "Do you suppose we could build a computer from this stuff?"

• The engineers among us might propose nano-molecular devices with fullerene switches, or even DNA-like computers.
• But I am sure that they would never think of neurons.
• Neurons are astronomically large structures compared to the molecules we are starting with

• Faced with the raw medium of carbon chemistry, and no knowledge of organic life,
• we would never think of brains built of neurons,
• supported by circulatory and digestive systems,
• in bodies with limbs for mobility,
• bodies which can only exist in the context of the ecological community that feeds them.

• We are in a similar position today as we face the raw medium of digital computation and communications.
• The preconceptions and limited imaginations deriving from our organic-only experience of life and intelligence,
• make it difficult for us to understand the nature of this new medium, and the forms of life and intelligence that might inhabit it

• How can we go beyond our conceptual limits,
• find the natural form of intelligent processes in the digital medium,
• and work with the medium to bring it to its full potential,
• rather than just imposing the world we know upon it by forcing it to run a simulation of our physics, chemistry, and biology?

• In the carbon medium it was evolution that explored the possibilities inherent in the medium, and created the human mind.
• Evolution listens to the medium that it is embedded in.
• It has the advantage of being mindless,
• and therefore devoid of preconceptions,
• and not limited by imagination.

• I propose the creation of a digital nature.
• A system of wildlife reserves in cyberspace
• in the interstices between human colonizations,
• feeding off of unused CPU-cycles
• and permitted a share of our bandwidth

• This would be a place where evolution can spontaneously generate complex information processes,
• free from the demands of human engineers and market analysts telling it what the target applications are.
• A place for a digital Cambrian explosion of diversity and complexity

• Digital naturalists can then explore this cyber-nature in search of applications for the products of digital evolution,
• in the same way that our ancestors found applications among the products of organic nature, such as: rice, wheat, corn, chickens, cows, pharmaceuticals, silk, mahogany.
• But, of course, the applications that we might find in the living digital world would not be material, they would be information processes.

• It is possible that out of this digital nature,
• there might emerge a digital intelligence,
• truly rooted in the nature of the medium,
• rather than brutishly copied and downloaded from organic nature.
• It would be a fundamentally alien intelligence,
• but one which would complement rather than duplicate our talents and abilities

• Concept - Motivation
• The Virtual Machine
• Using Tierra
• Tools
• The Ancestor
• Results
• Network Tierra
• Future Directions

• The virtual machine was named "Tierra", Spanish for "Earth"
• Originally, the only design criteria was that it should be able to support the evolution of self-replicating machine code
• It may have been the first Von Neuman computer designed for evolvability

• Self-replicating entities
• Turn-over of generations
• Genetic inheritance
• Genetic variation

• Darwinian Operating System
• Soup (RAM)
• CPU Structure
• Instruction Set
• Genetic Operations

• Darwinian Operating System
• Soup (RAM)
• CPU Structure
• Instruction Set
• Genetic Operations

• Manages a population of processes in a Darwinian fashion
• Includes the following elements:
• Slicer
• Reaper
• Memory Allocation
• Genetic Operations
• Disturbances

• Slicer
• Reaper
• Memory Allocation
• Genetic Operations
• Disturbances

• The Slicer is a circular queue of processes
• The Slicer allocates slices of CPU time to each process in the queue, in succession
• The size of the time slice determines the number of machine instructions that a process will execute in its turn
• The slice size may be fixed, or a uniform random variate, or dependent on the size of the process
• When a new process is born, it enters the queue behind its mother

• Slicer
• Reaper
• Memory Allocation
• Genetic Operations
• Disturbances

• The Reaper is a linear queue of processes
• At birth, processes enter the bottom of the queue
• When the memory is full, the Reaper kills processes at the top of the queue
• The Reaper removes the dead process from both the Reaper and the Slicer queues
• Memory allocated to the dead process is freed
• The code of the dead process is not removed from the soup

• In the first approximation, the oldest process dies first
• The Reaper may kill:
• The process at the top of the queue
• A process randomly selected from the top X% of the queue (death may be partially or fully random)
• When a process generates an error, it moves one position up the Reaper queue
• Successful execution of divide or mal moves the process one position down

• Slicer
• Reaper
• Memory Allocation
• Genetic Operations
• Disturbances

• Processes are born with a block of memory
• The memory may have read, write, or execute protection
• Default is only write protection, such that other processes may not write to the block
• Processes may request a second memory block, but no more
• A third memory request re-allocates the second block (data not copied)

• The memory allocator provides several options for placing the memory block:
• first fit
• better fit
• random preference
• near mother’s address
• suggested address

• The memory allocator is connected to the Reaper
• When a memory request cannot be fulfilled because a block of the requested size is not available,
• The Reaper kills processes until a block of the requested size becomes available
• The size of memory requests are limited to N times the size of the first block (N = 3)

• Slicer
• Reaper
• Memory Allocation
• Genetic Operations
• Disturbances

• There are three broad classes of genetic operations:
• Mutations
• Gene Splicing
• Flaws
• Genetic operations are applied at:
• The moment of birth of a new process, or
• Any time during the life of the process
• Genetic Operations in Tierra are documented at: http://www.hip.atr.co.jp/ ~ray/tierra/netreport/netreport.html#Genops

• Mutations
• Gene Splicing
• Flaws

• There are two kinds of mutations of machine instructions:
• bit flips - a single bit of the instruction is flipped (original Tierra 5 bits, Network 6 bits)
• random replacements - the affected instruction is replaced by one of the 32 (or 64) instructions in the set, chosen at random
• Mutations occur when:
• a process is born
• code is copied from place to place
• any time at random (cosmic ray)

• Mutations
• Gene Splicing
• Flaws

• There are three classes of splicing:
• Crossover
• Insertion
• Deletion
• Each class can occur in two ways:
• Anywhere in the genome
• Only at "segment boundaries", marked by templates
• Gene splicing is applied to a daughter process at the time of birth

• A "mate" is chosen at random for our "daughter" about to be born
• A crossover point in the daughter genome is chosen at random
• The smaller part of the daughter is replaced with the corresponding part of the mate
• Crossover can occur in two forms:
• preserving the size of the daughter
• potentially changing the size of the daughter

• Like crossover, insertion involves the selection of a mate for our daughter
• Unlike crossover, the code to be inserted does not replace code already in the daughter
• The code may be inserted an any location within the daughter’s genome
• Any proportion of the mate’s genome may be inserted into the daughter

• Up to one-half of the genome may be deleted.
• First the size of the segment to be deleted is chosen at random (0 to 1/2)
• Next the offset of the segment is determined within the genome
• The segment is removed from the genome

• Each class of gene splicing can occur in two ways:
• Anywhere in the genome
• Only at "segment boundaries", marked by templates

• Is an attempt to make splicing a little bit smart, by splicing functionally coherent chunks of code
• It is based on the recognition that in Tierra, control-flow (jump) points are marked by templates
• Segment boundary splicing cuts only at the location of templates

• Mutations
• Gene Splicing
• Flaws

• Flaws are not genetic operations, because they do not alter the genetic code
• Flaws were originally conceived of as being analogous to metabolic reactions gone wrong, or producing side products
• Flaws are "intentional" errors in the operations of the machine instructions
• Most flaws are errors of magnitude + or - 1
• Flaws are non-genetic noise in the system

• Flaws have been implemented for almost all of the machine instructions, e.g.:
• add adds the values of the data in two CPU registers
• the result may be flawed by + or - 1
• The results of all arithmetic operations may be incorrect by the amount + or - 1

• Instructions moving data to or from CPU registers may use an incorrect register, always a neighboring register
• Instructions shifting or rotating bits in registers may shift the bits one place too much or too little
• Instructions manipulating (e.g. flipping) bits may manipulate the wrong (neighboring) bit

• Slicer
• Reaper
• Memory Allocation
• Genetic Operations
• Disturbances

• The operating system may optionally kill a proportion of the population of processes at regular or irregular intervals
• The user can define the proportion killed, and the temporal pattern of the disturbances

• Darwinian Operating System
• Soup (RAM)
• CPU Structure
• Instruction Set
• Genetic Operations

• Memory is circular
• The size of the memory is set at startup, and can not change during a run

• Darwinian Operating System
• Soup (RAM)
• CPU Structure
• Instruction Set
• Genetic Operations

• Instruction Pointer
• Registers
• Stack
• Stack Pointer
• Flags

• There are four registers in original Tierra, six in Network Tierra
• The (10 word) stack is circular, repeated pushes wrap around and overwrite data.

• Darwinian Operating System
• Soup (RAM)
• CPU Structure
• Instruction Set
• Genetic Operations

• Graceful Error Handling
• Small (no numeric operands)
• Template Addressing
• (almost) No Syntax
• Otherwise Normal

• Graceful Error Handling
• Small (no numeric operands)
• Template Addressing
• (almost) No Syntax
• Otherwise Normal

• No instruction can generate an error that would crash the virtual machine
• Serious errors cause the instruction to fail to have any effect,
• and the instruction pointer moves on to the next instruction

• Graceful Error Handling
• Small (no numeric operands)
• Template Addressing
• (almost) No Syntax
• Otherwise Normal

Small Instruction Set
No Numeric Operands

• "Normal" machine codes permit instructions to include numeric operands
• The bit pattern that specifies the instruction must include bits to specify:
• which operation
• the numeric operands
• Most of the bits in machine instructions are used to specify the numeric operands.

• The size of the instruction set collapses to a very small number if numeric operands are not allowed
• The instructions can still operate on numbers stored in the CPU registers
• "Fixed" numbers can be created in the registers through bit manipulations, e.g., set-to-zero, flip low order bit, shift left

• Graceful Error Handling
• Small (no numeric operands)
• Template Addressing
• (almost) No Syntax
• Otherwise Normal

• Numeric operands would normally be used to specify addresses, such as absolute or relative addresses for the jump instruction.
• Because numeric operands can not be used for this purpose, another method is needed.
• In Tierra, the jump instruction uses a template rather than an absolute or relative address.

• Templates are an idea borrowed from molecular biology.
• Molecules "address" one another by having complementary shapes.
• Templates are complementary patterns of ones and zeros.
• Templates are built from two kinds of nop instructions: nop0 and nop1

• The instruction sequence: jmp nop0 nop0 nop1
• causes execution of the program to jump to the nearest occurrence of the instruction sequence: nop1 nop1 nop0
• Complementarity insures that the instruction sequence will not find a copy of itself.

• Graceful Error Handling
• Small (no numeric operands)
• Template Addressing
• (almost) No Syntax
• Otherwise Normal

• Except for instructions which use templates: adrb adrf adro call jmpb jmpf jmpo
• all instructions are "atomic", they do not require a context in relation to neighboring instructions.

• Graceful Error Handling
• Small (no numeric operands)
• Template Addressing
• (almost) No Syntax
• Otherwise Normal

• The instructions in the virtual machine code are mostly conventional: nop add and call clrflag dec div halt ifzero inc jmp join (threads) mal mov mul not ior pop push rand ret shl shr split (thread) sub xor zero get put
• Register usage of instructions is configured at run-time

• Concept - Motivation
• The Virtual Machine
• Using Tierra
• Tools
• The Ancestor
• Results
• Network Tierra
• Future Directions

• Obtaining Tierra
• Setting up Tierra
• Running Tierra

• Obtaining Tierra
• Setting up Tierra
• Running Tierra

• Obtaining Tierra
• Setting up Tierra
• Running Tierra

• copy the compressed archive into an empty directory
• gunzip tierraLinux.tar.gz
• tar xf tierraLinux.tar
• rm *.tar

• Obtaining Tierra
• Setting up Tierra
• Running Tierra

• Run Parameters
• Start Run
• Exit Run

• Run Parameters
• Start Run
• Exit Run

• GeneBnker = <flag>
• 0 = gene banker off
• 1 = gene banker on
• GenebankPath = <path>/
• path to gene bank directory (include ending "/")
• SaveFreq = <integer>
• frequency of automatic save (millions of instructions)

• TierraLog =< flag >
• 0 = logging off
• 1 = logging on
• alive = <integer>
• how many generations/instructions the run will continue
• 0 = no limit
• AliveGen = 0 (count instructions)
• AliveGen = 1 (count generations)

• DropDead = <integer>
• stop system if no reproduction in the last <integer> million instructions
• 0 =no limit
• NumCells = <integer>
• number of creatures used to inoculate new soup
• includes directives <ex: center, space>

• seed = <integer>
• seed for random number generator
• 0 = random seed
• SoupSize = <integer> size of soup in instructions

• directives
• space <integer> - skip <integer> locations before injecting next creature
• center - skip one-half of the soup size before injecting next creature
• genotype to be loaded (ex: 0080aaa)

• Run Parameters
• Start Run
• Exit Run

• new run
• tierra1 [soup_in]
• default is "soup_in" if "soup_in" file name is not specified
• tierra1 <soup_in> x
• stop at main menu before commencing run
• resume saved run
• tierra1 <gene bank dir>/soup_out

• Run Parameters
• Start Run
• Exit Run

• Quit
• Save and Quit

• Concept - Motivation
• The Virtual Machine
• Using Tierra
• Tools
• The Ancestor
• Results
• Network Tierra
• Future Directions

• Live Beagle Explorer
• Paleo Beagle Explorer
• Evolvability
• Tieout
• Probe

• The Beagle tools are named after Darwin’s exploratory vessel, the HMS Beagle.
• The concept is that this is the vehicle that takes us into the world of Tierra, and permits us to observe the evolution there.
• The Beagle tools can be divided into two classes:
• Live - which allow us to observe evolution in Tierra while it is running
• Paleo - which allow us to examine the data left by Tierra after it has finished running

• Live Beagle Explorer
• Paleo Beagle Explorer
• Evolvability
• Tieout
• Probe

• Main Window

• Main Window - File Menu

• Main Window - Connection Menu

• Create New Connection - By Host Name

• Status Window

• Plan Window

• Histograms

• Variables

• Overview

• Overview - Disassembly from Soup

• Debug Window - Break Point

• Debug Window - Run Mode

• Debug - Step Mode

• Messages

• Main Window - Misc Menu

• Misc Menu - Injection

• Live Beagle Explorer
• Paleo Beagle Explorer
• Evolvability
• Tieout
• Probe

• Paleo Beagle Explorer was the first observational tool developed for Tierra
• Beagle was developed in DOS
• Beagle used the Greenleaf DataWindows text-mode windowing system,
• and therefore eventually became frozen, and difficult to maintain (can only be compiled with the Turbo C V2.0 compiler)
• Paleo Beagle is currently being ported to Visual C++

• Includes several observational tools:
• Bar
• Trace
• Diversity
• Template
• Probe
• Prepare

• Includes several observational tools:
• Bar - reads break.# files and displays a moving histogram of size or genotype frequencies over time
• Trace
• Diversity
• Template
• Probe
• Prepare

• Includes several observational tools:
• Bar
• Trace - reads break.# files and displays the relative frequency over time of two size or genotype classes in a 2D x-y plot
• Diversity
• Template
• Probe
• Prepare

• Includes several observational tools:
• Bar
• Trace
• Diversity - reads break.# files and calculates and displays graphically a diversity index over time
• Template
• Probe
• Prepare

• Includes several observational tools:
• Template - reads ####.gen files and displays template usage of programs, give a rough overview of the control flow of the algorithm
• Probe - reads ####.gen files and compares the alignment of two genomes, allows quick comparison of evolutionary relationships and genetic change
• Prepare - prepares data for use with bar and trace, by previewing the range of the data

• Live Beagle Explorer
• Paleo Beagle Explorer
• Evolvability
• Tieout
• Probe

• Evolvability is a descendant of the diversity tool originally developed for Paleo Beagle
• Evolvability is currently under development as the primary analytical tool for an empirical study of evolvability in Tierra
• Evolvability is built in Visual C++

• Live Beagle Explorer
• Paleo Beagle Explorer
• Evolvability
• Tieout
• Probe

• Tieout reads the tierra.log file, and outputs two columns of values for any pair of data fields chosen from the tierra.log file.
• I use it primarily to show the change in size over time.
• Tieout is currently developed under Visual C++, and provides a 2D image of the output, as well as saving the output to a file

• Live Beagle Explorer
• Paleo Beagle Explorer
• Evolvability
• Tieout
• Probe

• The independent Probe tool is unrelated to the Paleo Beagle Probe tool
• Probe reads the ####.gen files
• Probe scans all .gen files in a genebank selecting genomes that match any set of criteria that you specify

• Evolvability, Tieout, and Probe are being folded into the Paleo Beagle Explorer
• Next, Live Beagle and Paleo Beagle will be merged into a single too.

• Concept - Motivation
• The Virtual Machine
• Using Tierra
• Tools
• The Ancestor
• Results
• Network Tierra
• Future Directions

• Concept - Motivation
• The Virtual Machine
• Using Tierra
• Tools
• The Ancestor
• Results
• Network Tierra
• Future Directions

• Emergence of Ecology
• Optimization
• Size decrease
• Loop unrolling
• Instruction Set Sensitivity

• Emergence of Ecology
• Optimization
• Size decrease
• Loop unrolling
• Instruction Set Sensitivity

• Emergence of Ecology
• Optimization
• Size decrease
• Loop unrolling
• Instruction Set Sensitivity

• Emergence of Ecology
• Optimization
• Size decrease
• Loop unrolling
• Instruction Set Sensitivity

• Emergence of Ecology
• Optimization
• Size decrease
• Loop unrolling
• Instruction Set Sensitivity

Copy loop of 80aaa
10 instructions executed per loop

Copy loop of 72etq
6 instructions per copy, 18 per loop

• Emergence of Ecology
• Optimization
• Size decrease
• Loop unrolling
• Instruction Set Sensitivity

• Concept - Motivation
• The Virtual Machine
• Using Tierra
• Tools
• The Ancestor
• Results
• Network Tierra
• Future Directions

• Motivation
• The Network Environment
• The Sensory System
• Transport Mechanisms
• Differentiated Multi-cellularity

• Motivation
• The Network Environment
• The Sensory System
• Transport Mechanisms
• Differentiated Multi-cellularity

• Motivation
• The Network Environment
• The Sensory System
• Transport Mechanisms
• Differentiated Multi-cellularity

• Motivation
• The Network Environment
• The Sensory System
• Transport Mechanisms
• Differentiated Multi-cellularity

• Motivation
• The Network Environment
• The Sensory System
• Transport Mechanisms
• Differentiated Multi-cellularity

• Processes are able to move to other machines on the network
• When a process moves to an other machine, it is removed from the first machine
• A mother may send her daughter at birth
• A process may move at any time in its life

• Motivation
• The Network Environment
• The Sensory System
• Transport Mechanisms
• Differentiated Multi-cellularity

• Concept - Motivation
• The Virtual Machine
• Using Tierra
• Tools
• The Ancestor
• Results
• Network Tierra
• Future Directions

• MS Windows Environment
• Broadband Network Tierra
• Public Release of Network Tierra
• Large Scale Tests
• Wildlife Reserve in Cyberspace

• MS Windows Environment
• Broadband Network Tierra
• Public Release of Network Tierra
• Large Scale Tests
• Wildlife Reserve in Cyberspace

• Tierra was originally developed as a 16 bit DOS application using Turbo C V1.0
• Tierra was then converted to a 32 bit application for both DOS and UNIX
• Eventually Tierra came to be supported on a wide variety of platforms: DOS, Amiga, Win95, WinNT, every flavor of UNIX, VMS, intermittent Mac support

• As a research project, Tierra has been developed primarily under UNIX
• Now the notebook PC on my desk runs ten times as fast as the Sparc station on my desk
• Thus we are shifting our emphasis to the WIntel environment
• Tierra and all tools are being ported to Visual C++ and fully supported under WIntel

• MS Windows Environment
• Broadband Network Tierra
• Public Release of Network Tierra
• Large Scale Tests
• Wildlife Reserve in Cyberspace

• The greatest technical problem in the development of Network Tierra has been the limitation of network bandwidth
• We have had to make many design compromises and modifications in the face of this reality
• It appears that broadband network service will become widely available in the next few years
• This will permit a more natural development of Network Tierra

• MS Windows Environment
• Broadband Network Tierra
• Public Release of Network Tierra
• Large Scale Tests
• Wildlife Reserve in Cyberspace

• Network Tierra has not been released because of:
• bandwidth limitations
• the need for a mechanism to control entry into the network during development and testing
• We hope to overcome both of these obstacles and release Network Tierra by the summer of 2000

• MS Windows Environment
• Broadband Network Tierra
• Public Release of Network Tierra
• Large Scale Tests
• Wildlife Reserve in Cyberspace

• The public release of Network Tierra will permit large scale tests involving thousands of participating machines joined into large experiments

• MS Windows Environment
• Broadband Network Tierra
• Public Release of Network Tierra
• Large Scale Tests
• Wildlife Reserve in Cyberspace

• The ultimate goal of Network Tierra is to become a permanent wildlife reserve for digital organisms in cyberspace
• It will be a place where evolution in the digital medium can spontaneously generate diversity and complexity of digital organisms without human interference

• This presentation: http://www.hip.atr.co.jp/~ray/pubs/pubs.html http://www.hip.atr.co.jp/~ray/pubs/tutorial/Tutorial.ppt
• Tierra Home Page: http://www.hip.atr.co.jp/~ray/tierra/tierra.html
• Tom Ray: tray@ou.edu http://www.hip.atr.co.jp/~ray/
• Joseph Hart: jhart@hip.atr.co.jp http://www.hip.atr.co.jp/~jhart/