// Strategy:
// a) Match the prefix and suffix of the language with the x and z
// b) See if y can be pumped against the middle part
// The horrifying part is the quantifiers
public static bool splitGood(Split split, ArithmeticLanguage language, BooleanExpression additionalConstraint)
{
// We just need to find a k such that (x y^k z) \not\in L
// If we cannot find such a k for some p, it is a bad split
// Say i, j are the variables in the language constraint and
// v_1, v_2 are variables in split constraints
// Therefore, if for all p, v_1, \ldots, v_n that satisfies split constraints
// and additional constraints and exists k such that for all i, j language
// constraint does not hold, then split is bad
Console.WriteLine("\t\tSplit is good if none of the following mids can be pumped: ");
// We will definitely go through the loop at least once as match is working
var beginningMatches = Matcher
.match(split.start, language.symbolic_string)
.Where(x => !x.FirstRemaining)
.Select(x => x.withAdditionalConstraint(language.constraint))
.Select(x => x.withAdditionalConstraint(additionalConstraint))
.Where(x => x.isFeasible());
foreach (var beginMatch in beginningMatches)
{
var remainingLanguage = beginMatch.remaining2;
var endMatches = Matcher
.match(split.end.reverse(), remainingLanguage.reverse())
.Where(x => !x.FirstRemaining)
.Select(x => x.withAdditionalConstraint(language.constraint))
.Select(x => x.withAdditionalConstraint(additionalConstraint))
.Where(x => x.isFeasible());
foreach (var endMatch in endMatches)
{
var fullConstraint = LogicalExpression.And(beginMatch.constraint, endMatch.constraint);
if (!fullConstraint.isSatisfiable())
{
continue;
}
var midLanguage = endMatch.remaining2.reverse();
var midSplit = split.mid;
var ctx = new Context();
// Console.WriteLine("\t\t" + midLanguage + " ===== " + midSplit + " when " + fullConstraint);
// var z3exp = fullConstraint.toZ3(ctx).Simplify();
// Console.WriteLine("\t\t" + midLanguage + " ===== " + midSplit + " when " + z3exp);
if (!canMismatchOne(midLanguage, midSplit, fullConstraint))
{
return(false);
}
}
}
return(true);
}
public static bool NonRegularCheckI(ArithmeticLanguage language, string start, string mid, string end, int i)
{
string fullWord = pumpMid(start, mid, end, i);
if (language.symbolic_string.isFlat())
{
SymbolicString wordSS = Parser.parseSymbolicString(fullWord.ToString(), language.alphabet.ToList());
return(ProofChecker.checkContainment(wordSS, language, LogicalExpression.True()));
}
else
{
throw new PumpingLemmaException("Arithmetic Language must be flat!");
}
}
public static bool check(ArithmeticLanguage language, SymbolicString pumpingString)
{
if (pumpingString.GetIntegerVariables().Count() != 1)
{
return(false);
}
var pumpingLength = pumpingString.GetIntegerVariables().First();
var pumpingLengthVariable = PumpingLemma.LinearIntegerExpression
.SingleTerm(1, pumpingLength);
var additionalConstraint = LogicalExpression.And(
PumpingLemma.ComparisonExpression.GreaterThan(pumpingLengthVariable, 0),
LogicalExpression.And(pumpingString.repeats().Select(x => ComparisonExpression.GreaterThanOrEqual(x, 0)))
);
// 0. Need to check if pumping string grows unboundedly with p
var pumpingStringLength = pumpingString.length();
if (pumpingStringLength.isConstant() || pumpingStringLength.coefficients[pumpingLength] < 0)
{
return(false);
}
foreach (var r in pumpingString.repeats())
{
if (r.coefficients[pumpingLength] < 0)
{
return(false);
}
}
// 1. Check that the pumping string is in the language for all p
if (!checkContainment(pumpingString, language, additionalConstraint))
{
return(false);
}
Console.WriteLine("Language is non-regular if all the following splits are good:");
int i = 0;
// 2. Check that each split of the pumping string has an valid pumping length
foreach (var split in pumpingString.ValidSplits(pumpingLengthVariable, additionalConstraint))
{
Console.WriteLine("\t" + (i++) + ": " + split + " when " + additionalConstraint);
if (!splitGood(split, language, additionalConstraint))
{
return(false);
}
}
return(true);
}
private static IEnumerable <Match> matchConcatConcat(SymbolicString s1, SymbolicString s2)
{
if (s1.isEpsilon() || s2.isEpsilon())
{
yield return(Match.MakeMatch(LogicalExpression.True(), s1, s2));
yield break;
}
// Quick match prefix symbols
int i;
for (i = 0; i < s1.sub_strings.Count && i < s2.sub_strings.Count; i++)
{
if (s1.sub_strings[i].expression_type != SymbolicString.SymbolicStringType.Symbol ||
s2.sub_strings[i].expression_type != SymbolicString.SymbolicStringType.Symbol)
{
break;
}
if (s1.sub_strings[i].atomic_symbol != s2.sub_strings[i].atomic_symbol)
{
yield break;
}
}
var sub1 = s1.sub_strings.Skip(i);
var sub2 = s2.sub_strings.Skip(i);
// If we have consumed something fully, just return the remaining bits
if (i == s1.sub_strings.Count || i == s2.sub_strings.Count)
{
yield return(Match.MakeMatch(
LogicalExpression.True(),
SymbolicString.Concat(sub1),
SymbolicString.Concat(sub2)));
yield break;
}
var rest1 = SymbolicString.Concat(sub1.Skip(1));
var rest2 = SymbolicString.Concat(sub2.Skip(1));
foreach (var m in match(sub1.First(), sub2.First()))
{
foreach (var mp in m.continueMatch(rest1, rest2))
{
yield return(mp);
}
}
}
public static string NonRegularGetUnpumpableWord(ArithmeticLanguage language, SymbolicString unpumpableWord, int n)
{
Dictionary <VariableType, int> assignment = new Dictionary <VariableType, int>();
assignment.Add(VariableType.Variable("n"), n);
string word = pumpedWord(unpumpableWord, assignment);
SymbolicString ss = SymbolicString.FromTextDescription(language.alphabet.ToList(), word);
while (!ProofChecker.checkContainment(ss, language, LogicalExpression.True()))
{
assignment[VariableType.Variable("n")]++;
word = pumpedWord(unpumpableWord, assignment);
ss = SymbolicString.FromTextDescription(language.alphabet.ToList(), word);
}
return(word);
}
private static IEnumerable <Match> matchSymbolConcat(SymbolicString s1, SymbolicString s2)
{
if (s2.isEpsilon())
{
yield return(Match.PartialFirst(LogicalExpression.True(), s1));
yield break;
}
var rest = SymbolicString.Concat(s2.sub_strings.Skip(1));
foreach (var m in match(s1, s2.sub_strings.First()))
{
foreach (var mp in m.continueMatch(SymbolicString.Epsilon(), rest))
{
yield return(mp);
}
}
}
// Either consume symbol with first symbol of repeat and say repeat is positive
// Or don't consume symbol and say repeat is zero
private static IEnumerable <Match> matchSymbolRepeat(SymbolicString s1, SymbolicString s2)
{
Debug.Assert(s2.isFlat());
// When repeat is 0
yield return(Match.PartialFirst(ComparisonExpression.Equal(s2.repeat, 0), s1));
// When repeat is non-zero
foreach (var m in match(s1, s2.root))
{
// Because the root is a word, we immediately know if the symbol matches or not
// and get an m if and only if the symbol matches
Debug.Assert(!m.FirstRemaining);
yield return(Match.PartialSecond(
LogicalExpression.And(m.constraint, ComparisonExpression.GreaterThan(s2.repeat, 0)),
SymbolicString.Concat(m.remaining2, SymbolicString.Repeat(s2.root, s2.repeat - 1))
));
}
}
private static IEnumerable <Match> shortLeftMatches(SymbolicString s1, SymbolicString s2, int firstMismatch)
{
int l1 = s1.root.wordLength();
for (int i = 1; l1 *i <= firstMismatch; i++)
{
var s1r = SymbolicString.Concat(Enumerable.Repeat(s1.root, i));
foreach (var m in match(s1r, s2))
{
if (m.FirstRemaining)
{
continue;
}
yield return(m.withAdditionalConstraint(LogicalExpression.And(
ComparisonExpression.Equal(s1.length(), s1r.length()),
ComparisonExpression.GreaterThan(m.remaining2.length(), 0)
)));
}
}
}
public Match forceFinish()
{
BooleanExpression additionalConstraint = LogicalExpression.True();
if (FirstRemaining)
{
additionalConstraint = LogicalExpression.And(
additionalConstraint,
ComparisonExpression.Equal(remaining1.length(), 0)
);
}
if (SecondRemaining)
{
additionalConstraint = LogicalExpression.And(
additionalConstraint,
ComparisonExpression.Equal(remaining2.length(), 0)
);
}
return(FullMatch(LogicalExpression.And(this.constraint, additionalConstraint)));
}
// Generates splits (x, y, z) such that |y| > 0 and |xy| < p
public IEnumerable <Split> ValidSplits(
LinearIntegerExpression pumpingLengthVariable,
BooleanExpression additionalConstraints)
{
foreach (var split in this.Splits())
{
if (split.mid.isEpsilon())
{
continue;
}
var cond1 = ComparisonExpression.GreaterThan(split.mid.length(), LinearIntegerExpression.Constant(0));
var cond2 = ComparisonExpression.LessThan(split.start.length() + split.mid.length(), pumpingLengthVariable);
var condition = LogicalExpression.And(additionalConstraints, cond1, cond2);
if (condition.isMaybeSatisfiable())
{
split.AddConstraint(condition);
yield return(split);
}
}
}
public static int NonRegularGetI(ArithmeticLanguage language, string start, string mid, string end)
{
SymbolicString matchingString = splitToSymbStr(language.alphabet.ToList(), start, mid, end);
if (ProofChecker.checkContainment(matchingString, language, LogicalExpression.True()))
{
return(1); // AI surrenders
}
else
{
int i = 0;
do
{
string word = pumpMid(start, mid, end, i);
SymbolicString ss = SymbolicString.FromTextDescription(language.alphabet.ToList(), word);
if (!ProofChecker.checkContainment(ss, language, LogicalExpression.True()))
{
return(i);
}
i++;
} while (i < 99); //for debugging purposes
return(-1);
}
}
public void AddConstraint(BooleanExpression c)
{
this.constraints = LogicalExpression.And(this.constraints, c);
}
public static BooleanExpression And(IEnumerable <BooleanExpression> ops)
{
return(ops.Aggregate(LogicalExpression.True() as BooleanExpression, (x, y) => And(x, y)));
}
// Generate TwoSplit's where either one may be empty
// Generates the splits in order, i.e., by length of the prefix
// So, for s being symbol and concat, first one will always be (\epsilon, s) and last one always (s, \epsilon)
// So, for s being repeat (abc)^n, first will be ((abc)^i,(abc)^j) and last one always ((abc)^i ab, c(abc)^j)
// Requires a flat symbolic string
public IEnumerable <TwoSplit> TwoSplits()
{
SymbolicString prefix, suffix;
// Contract.Requires(this.isFlat());
switch (this.expression_type)
{
case SymbolicStringType.Symbol:
yield return(TwoSplit.MakeSplit(SymbolicString.Epsilon(), this, LogicalExpression.True()));
yield return(TwoSplit.MakeSplit(this, SymbolicString.Epsilon(), LogicalExpression.True()));
break;
case SymbolicStringType.Concat:
yield return(TwoSplit.MakeSplit(SymbolicString.Epsilon(), this, LogicalExpression.True()));
for (int i = 0; i < this.sub_strings.Count; i++)
{
prefix = SymbolicString.Concat(this.sub_strings.Take(i).ToList());
suffix = SymbolicString.Concat(this.sub_strings.Skip(i + 1).ToList());
foreach (var split in this.sub_strings[i].TwoSplits())
{
if (!split.start.isEpsilon())
{
yield return(split.extend(prefix, suffix));
}
}
}
break;
case SymbolicStringType.Repeat:
var v1 = LinearIntegerExpression.FreshVariable();
var v2 = LinearIntegerExpression.FreshVariable();
var sanityConstraint = LogicalExpression.And(
ComparisonExpression.GreaterThanOrEqual(v1, 0),
ComparisonExpression.GreaterThanOrEqual(v2, 0)
);
prefix = SymbolicString.Repeat(this.root, v1);
suffix = SymbolicString.Repeat(this.root, v2);
yield return(TwoSplit.MakeSplit(
prefix,
suffix,
LogicalExpression.And(sanityConstraint, ComparisonExpression.Equal(v1 + v2, this.repeat))
));
if (this.root.expression_type != SymbolicStringType.Concat)
{
break;
}
for (int i = 1; i < this.root.sub_strings.Count; i++)
{
var split = TwoSplit.MakeSplit(
SymbolicString.Concat(this.root.sub_strings.Take(i)),
SymbolicString.Concat(this.root.sub_strings.Skip(i)),
LogicalExpression.And(
ComparisonExpression.Equal(v1 + v2 + 1, this.repeat),
sanityConstraint
)
);
yield return(split.extend(prefix, suffix));
}
break;
default:
throw new ArgumentOutOfRangeException();
}
}
// Generates splits where all three parts may be empty
public IEnumerable <Split> Splits()
{
// Contract.Requires<ArgumentException>(this.isFlat());
switch (this.expression_type)
{
case SymbolicStringType.Symbol:
yield return(Split.MakeSplit(this, SymbolicString.Epsilon(), SymbolicString.Epsilon(), LogicalExpression.True()));
yield return(Split.MakeSplit(SymbolicString.Epsilon(), this, SymbolicString.Epsilon(), LogicalExpression.True()));
yield return(Split.MakeSplit(SymbolicString.Epsilon(), SymbolicString.Epsilon(), this, LogicalExpression.True()));
break;
case SymbolicStringType.Repeat:
var v1 = LinearIntegerExpression.FreshVariable();
var v2 = LinearIntegerExpression.FreshVariable();
var v3 = LinearIntegerExpression.FreshVariable();
var sanityConstraint = LogicalExpression.And(
ComparisonExpression.GreaterThanOrEqual(v1, 0),
ComparisonExpression.GreaterThanOrEqual(v2, 0),
ComparisonExpression.GreaterThanOrEqual(v3, 0)
);
// Suppose the word w = a_0 a_1 \ldots a_{n-1}
// All splits are of the form
// BEG: (a_0 \ldots a_{n-1})^i (a_0 \ldots a_p) = w^i . w_1
// MID: (a_{p+1} \ldots a_{n-1} a_0 \ldots a_p)^j (a_{p+1} \ldots a_q) = (w_2 w_1)^j w_3
// END: (a_{q+1} \ldots a_{n-1}) (a_0 \ldots a_{n-1})^k = w_4 w^k
var w = this.root.wordSymbols();
var ww = w.Concat(w);
int n = w.Count();
for (int w1len = 0; w1len < n; w1len++)
{
var w_1 = w.Take(w1len);
var w_2 = w.Skip(w1len);
var beg = SymbolicString.Concat(
SymbolicString.Repeat(this.root, v1),
SymbolicString.Concat(w_1));
var mid_root = SymbolicString.Concat(
SymbolicString.Concat(w_2),
SymbolicString.Concat(w_1));
var mid_beg = SymbolicString.Repeat(mid_root, v2);
for (int w3len = 0; w3len < n; w3len++)
{
var w_3 = ww.Skip(w1len).Take(w3len);
var mid = SymbolicString.Concat(mid_beg, SymbolicString.Concat(w_3.ToList()));
IEnumerable <SymbolicString> w_4;
if (w1len + w3len == 0)
{
w_4 = new List <SymbolicString>();
}
else if (w1len + w3len <= n)
{
w_4 = w.Skip(w1len).Skip(w3len);
}
else
{
w_4 = ww.Skip(w1len).Skip(w3len);
}
var end = SymbolicString.Concat(
SymbolicString.Concat(w_4.ToList()),
SymbolicString.Repeat(this.root, v3)
);
var consumed = (w_1.Count() + w_3.Count() + w_4.Count()) / w.Count();
yield return(Split.MakeSplit(
beg,
mid,
end,
LogicalExpression.And(
ComparisonExpression.Equal(v1 + v2 + v3 + consumed, this.repeat),
sanityConstraint
)
));
}
}
break;
case SymbolicStringType.Concat:
foreach (var beg_midend in this.TwoSplits())
{
foreach (var mid_end in beg_midend.end.TwoSplits())
{
yield return(Split.MakeSplit(
beg_midend.start,
mid_end.start,
mid_end.end,
LogicalExpression.And(beg_midend.constraints, mid_end.constraints)));
}
}
break;
default:
throw new ArgumentOutOfRangeException();
}
}
// Generates XML for the
public XElement SplitDisplayXML(
VariableType pumpingLength,
BooleanExpression additionalConstraints)
{
Contract.Assert(additionalConstraints.GetVariables().Count() <= 1);
if (additionalConstraints.GetVariables().Count == 1)
{
Contract.Assert(additionalConstraints.GetVariables().First().Equals(pumpingLength));
}
var pumpingLengthVariable = LinearIntegerExpression.SingleTerm(1, pumpingLength);
var repeatLengths = repeats();
// For great and inexplicable reasons. Trust me, it looks better this way.
var displayConstraints = LogicalExpression.And(repeatLengths.Select(x =>
ComparisonExpression.GreaterThanOrEqual(x, LinearIntegerExpression.Constant(5))
));
XElement symbstrings = new XElement("symbstrings");
foreach (var split in this.ValidSplits(pumpingLengthVariable, additionalConstraints))
{
var splitRepeatLengths = split.start.repeats();
splitRepeatLengths.AddRange(split.mid.repeats());
splitRepeatLengths.AddRange(split.end.repeats());
// Get models that don't look terrible
var splitDisplayConstraints = LogicalExpression.And(splitRepeatLengths.Select(x =>
ComparisonExpression.GreaterThanOrEqual(x, LinearIntegerExpression.Constant(1))
));
var constraint = LogicalExpression.And(displayConstraints, split.constraints, splitDisplayConstraints);
if (!constraint.isSatisfiable())
{
continue;
}
var splitModel = constraint.getModel();
var symbstr = new XElement("symbstr");
var strings = new XElement("strings");
var splits = new XElement("splits");
var constrs = new XElement("constraints");
Func <string, Tuple <int, int, SymbolicString>, XElement> handleSegment = (parentTagName, segment) => {
var parent = new XElement(parentTagName);
var from = new XElement("from"); from.Value = segment.Item1.ToString();
var to = new XElement("to"); to.Value = segment.Item2.ToString();
var label = new XElement("label"); label.Add(segment.Item3.ToDisplayXML());
parent.Add(from);
parent.Add(to);
parent.Add(label);
return(parent);
};
int strIndex = 0;
foreach (var segment in getSegments(splitModel, ref strIndex))
{
strings.Add(handleSegment("string", segment));
}
int splitIndex = 0;
foreach (var segment in new[] { split.start, split.mid, split.end })
{
splits.Add(handleSegment("split", segment.makeSegment(splitModel, ref splitIndex)));
}
var constr = new XElement("constraint");
constr.Add(split.constraints.ToDisplayXML());
constrs.Add(constr);
symbstr.Add(strings);
symbstr.Add(splits);
symbstr.Add(constrs);
symbstrings.Add(symbstr);
}
return(symbstrings);
}
public static BooleanExpression Implies(BooleanExpression op1, BooleanExpression op2)
{
return(LogicalExpression.Or(LogicalExpression.Not(op1), op2));
}
public static ArithmeticLanguage FromTextDescriptions(List <String> alphabet, string symbolicStringText, string constraintText)
{
var symbolPattern = new Regex(@"^[a-zA-Z0-9]$");
var illegalSymbols = alphabet.FindAll(s => !symbolPattern.IsMatch(s));
if (illegalSymbols.Count > 0)
{
var message = string.Format(
"Found illegal symbols {0} in alphabet. Symbols should match [a-zA-Z0-9]",
string.Join(", ", illegalSymbols)
);
throw new PumpingLemmaException(message);
}
// Parse the language
var ss = PumpingLemma.Parser.parseSymbolicString(symbolicStringText, alphabet);
if (ss == null)
{
throw new PumpingLemmaException("Unable to parse language");
}
// Parse the constraintDesc
var constraint = PumpingLemma.Parser.parseCondition(constraintText);
if (constraint == null)
{
throw new PumpingLemmaException("Unable to parse constraint");
}
// Make sure all the variables are bound
var boundVariables = ss.GetIntegerVariables();
var constraintVariables = constraint.GetVariables();
// Console.WriteLine("Bound variables: " + String.Join(", ", boundVariables));
// Console.WriteLine("Constriant variables: " + String.Join(", ", constraintVariables));
foreach (var consVar in constraintVariables)
{
if (!boundVariables.Contains(consVar))
{
throw new PumpingLemmaException(
string.Format("Constraint variable {0} not bound", consVar));
}
}
// Add constraints saying that all variables are >= 0
BooleanExpression defaultConstraint = LogicalExpression.True();
foreach (var consVar in constraintVariables)
{
defaultConstraint = LogicalExpression.And(
defaultConstraint,
ComparisonExpression.GreaterThanOrEqual(
LinearIntegerExpression.SingleTerm(1, consVar),
LinearIntegerExpression.Constant(0)
)
);
}
return(new ArithmeticLanguage(alphabet, ss, constraint));
}
public static BooleanExpression And(params BooleanExpression[] ops)
{
return(ops.Aggregate(LogicalExpression.True() as BooleanExpression, (x, y) => And(x, y)));
}