295 lines
4.2 KiB
Plaintext
295 lines
4.2 KiB
Plaintext
# turingsim
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a quick and dirty turing machine simulator, written in C89.
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# the code
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=> https://tildegit.org/sejo/turingsim turingsim git repository
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```
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#include <stdio.h>
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#define TAPE_SIZE 80
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#define RULES_SIZE 256
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typedef struct {
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char state; /* current state */
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char symbol; /* current symbol */
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int head; /* index of head */
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char tape[TAPE_SIZE]; /* tape of characters */
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int nrules; /* number of rules */
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/* state, symbol, new state, new symbol, direction (even right, odd left ) */
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char rules[RULES_SIZE][5];
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} Machine;
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Machine m;
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int nsteps;
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int main(int argc, char *argv[]){
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int i,n=0;
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FILE *f;
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if(!(f = fopen(argv[1], "r"))){
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fprintf(stderr, "failed to load file\n");
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return 1;
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}
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printf("%s\n\n", argv[1]);
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/* read machine description */
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printf("initial state: ");
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fscanf(f,"%c",&m.state);
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printf("%c\n",m.state);
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printf("initial tape: ");
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fscanf(f,"%s",m.tape);
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printf("%s\n",m.tape);
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printf("initial position of head: ");
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fscanf(f,"%d",&m.head);
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m.head = (m.head+TAPE_SIZE)%TAPE_SIZE;
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printf("%d\n",m.head);
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printf("number of rules: ");
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fscanf(f,"%d",&m.nrules);
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printf("%d\n",m.nrules);
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for(i=0; i<m.nrules; i++){
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printf("rule number %d: ",i);
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fscanf(f,"%s",m.rules[i]);
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printf("%s\n",m.rules[i]);
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}
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printf("max number of simulation steps: ");
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fscanf(f,"%d",&nsteps);
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printf("%d\n\n",nsteps);
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/* simulate */
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int irules; /* rules index */
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do{
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printf("step %d\n",n);
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/* print head and state */
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for(i=0; i<m.head; i++)
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printf(" ");
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printf("%c\n",m.state);
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/* print tape: */
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printf("%s\n",m.tape);
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/* get symbol at head position */
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m.symbol = m.tape[ m.head ];
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/* search for corresponding rule */
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irules = -1;
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for(i=0; i<m.nrules && irules<0; i++)
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if(m.rules[i][0] == m.state && m.rules[i][1] == m.symbol)
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irules = i;
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if( irules == -1) /* halt if not found */
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printf("halted\n");
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else{ /* update machine otherwise */
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m.state = m.rules[irules][2]; /* new state */
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m.tape[ m.head ] = m.rules[irules][3]; /* new symbol */
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/* move head */
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if( m.rules[irules][4]%2 ) /* if odd, move to left */
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m.head = (m.head-1+TAPE_SIZE)%TAPE_SIZE;
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else /* if even, move to right */
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m.head = (m.head+1)%TAPE_SIZE;
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}
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printf("\n");
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}while( ++n<nsteps && irules != -1);
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return 0;
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}
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```
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# build and run
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to build:
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```
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cc -std=c89 -Wall turingsim.c -o turingsim
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```
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to run with an input file:
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```
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./turingsim parentesis.txt | less
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```
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# input file fields
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the line-based fields are:
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* initial state
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* inital tape
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* initial position of head on tape (starting at 0)
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* number of rules
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* list of rules, in the form: state, symbol, new state, new symbol, direction (even is right, odd is left)
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* maximum number of simulation steps
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# example input file
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this input file corresponds to the "comprobador de paréntesis" machine described in {máquinas de turing}
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```
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a
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A(()())A
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1
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11
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a)bX1
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a(a(0
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aAcA1
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aXaX0
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b)b)1
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b(aX0
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bAH00
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bXbX1
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c(H00
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cAH10
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cXcX1
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80
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```
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## example output
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the output for this example file looks as follows:
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```
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parentesis.txt
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initial state: a
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initial tape: A(()())A
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initial position of head: 1
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number of rules: 11
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rule number 0: a)bX1
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rule number 1: a(a(0
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rule number 2: aAcA1
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rule number 3: aXaX0
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rule number 4: b)b)1
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rule number 5: b(aX0
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rule number 6: bAH00
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rule number 7: bXbX1
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rule number 8: c(H00
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rule number 9: cAH10
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rule number 10: cXcX1
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max number of simulation steps: 80
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step 0
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a
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A(()())A
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step 1
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a
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A(()())A
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step 2
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a
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A(()())A
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step 3
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b
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A((X())A
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step 4
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a
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A(XX())A
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step 5
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a
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A(XX())A
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step 6
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a
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A(XX())A
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step 7
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b
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A(XX(X)A
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step 8
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a
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A(XXXX)A
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step 9
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a
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A(XXXX)A
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step 10
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b
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A(XXXXXA
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step 11
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b
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A(XXXXXA
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step 12
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b
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A(XXXXXA
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step 13
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b
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A(XXXXXA
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step 14
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b
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A(XXXXXA
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step 15
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a
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AXXXXXXA
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step 16
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a
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AXXXXXXA
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step 17
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a
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AXXXXXXA
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step 18
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a
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AXXXXXXA
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step 19
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a
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AXXXXXXA
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step 20
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a
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AXXXXXXA
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step 21
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c
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AXXXXXXA
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step 22
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c
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AXXXXXXA
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step 23
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c
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AXXXXXXA
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step 24
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c
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AXXXXXXA
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step 25
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c
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AXXXXXXA
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step 26
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c
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AXXXXXXA
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step 27
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c
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AXXXXXXA
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step 28
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H
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1XXXXXXA
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halted
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```
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the 1 written at the end indicates that the parenthesis sequence was well-formed. if there was a parenthesis without its pair, the machine would have written 0 instead.
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