/usr/bin/java -Xmx8000000000 -Xss4m -jar ./plugins/org.eclipse.equinox.launcher_1.5.800.v20200727-1323.jar -data @noDefault -ultimatedata ./data -tc ../../../trunk/examples/toolchains/BuchiAutomizerCInline.xml -s ../../../trunk/examples/settings/default/automizer/svcomp-Termination-32bit-Automizer_Default.epf --buchiautomizer.fairness.type.for.concurrent.programs FAIRNESS_INTERSECTION -i ../../../trunk/examples/svcomp/weaver/chl-word-trans.wvr.c -------------------------------------------------------------------------------- This is Ultimate 0.2.3-wip.me.fairness-42053ae-m [2023-09-08 14:42:16,284 INFO L172 SettingsManager]: Resetting all preferences to default values... [2023-09-08 14:42:16,325 INFO L100 SettingsManager]: Loading settings from /storage/repos/ultimate/releaseScripts/default/UAutomizer-linux/../../../trunk/examples/settings/default/automizer/svcomp-Termination-32bit-Automizer_Default.epf [2023-09-08 14:42:16,344 INFO L114 SettingsManager]: Preferences different from defaults after loading the file: [2023-09-08 14:42:16,344 INFO L135 SettingsManager]: Preferences of UltimateCore differ from their defaults: [2023-09-08 14:42:16,345 INFO L137 SettingsManager]: * Log level for class=de.uni_freiburg.informatik.ultimate.lib.smtlibutils.quantifier.QuantifierPusher=ERROR; [2023-09-08 14:42:16,346 INFO L135 SettingsManager]: Preferences of BlockEncodingV2 differ from their defaults: [2023-09-08 14:42:16,346 INFO L137 SettingsManager]: * Create parallel compositions if possible=false [2023-09-08 14:42:16,347 INFO L137 SettingsManager]: * Use SBE=true [2023-09-08 14:42:16,348 INFO L135 SettingsManager]: Preferences of BuchiAutomizer differ from their defaults: [2023-09-08 14:42:16,348 INFO L137 SettingsManager]: * NCSB implementation=INTSET_LAZY3 [2023-09-08 14:42:16,348 INFO L137 SettingsManager]: * Use old map elimination=false [2023-09-08 14:42:16,349 INFO L137 SettingsManager]: * Use external solver (rank synthesis)=false [2023-09-08 14:42:16,349 INFO L137 SettingsManager]: * Use only trivial implications for array writes=true [2023-09-08 14:42:16,349 INFO L137 SettingsManager]: * Rank analysis=LINEAR_WITH_GUESSES [2023-09-08 14:42:16,349 INFO L135 SettingsManager]: Preferences of CACSL2BoogieTranslator differ from their defaults: [2023-09-08 14:42:16,349 INFO L137 SettingsManager]: * sizeof long=4 [2023-09-08 14:42:16,350 INFO L137 SettingsManager]: * Check unreachability of error function in SV-COMP mode=false [2023-09-08 14:42:16,350 INFO L137 SettingsManager]: * Overapproximate operations on floating types=true [2023-09-08 14:42:16,350 INFO L137 SettingsManager]: * sizeof POINTER=4 [2023-09-08 14:42:16,350 INFO L137 SettingsManager]: * Check division by zero=IGNORE [2023-09-08 14:42:16,350 INFO L137 SettingsManager]: * Pointer to allocated memory at dereference=ASSUME [2023-09-08 14:42:16,351 INFO L137 SettingsManager]: * If two pointers are subtracted or compared they have the same base address=ASSUME [2023-09-08 14:42:16,351 INFO L137 SettingsManager]: * Check array bounds for arrays that are off heap=ASSUME [2023-09-08 14:42:16,351 INFO L137 SettingsManager]: * sizeof long double=12 [2023-09-08 14:42:16,351 INFO L137 SettingsManager]: * Check if freed pointer was valid=false [2023-09-08 14:42:16,351 INFO L137 SettingsManager]: * Assume nondeterminstic values are in range=false [2023-09-08 14:42:16,352 INFO L137 SettingsManager]: * Use constant arrays=true [2023-09-08 14:42:16,352 INFO L137 SettingsManager]: * Pointer base address is valid at dereference=ASSUME [2023-09-08 14:42:16,352 INFO L135 SettingsManager]: Preferences of RCFGBuilder differ from their defaults: [2023-09-08 14:42:16,352 INFO L137 SettingsManager]: * Size of a code block=SequenceOfStatements [2023-09-08 14:42:16,352 INFO L135 SettingsManager]: Preferences of TraceAbstraction differ from their defaults: [2023-09-08 14:42:16,352 INFO L137 SettingsManager]: * Trace refinement strategy=CAMEL [2023-09-08 14:42:16,353 INFO L137 SettingsManager]: * Apply one-shot large block encoding in concurrent analysis=false [2023-09-08 14:42:16,354 INFO L135 SettingsManager]: Preferences of IcfgTransformer differ from their defaults: [2023-09-08 14:42:16,354 INFO L137 SettingsManager]: * TransformationType=MODULO_NEIGHBOR WARNING: An illegal reflective access operation has occurred WARNING: Illegal reflective access by com.sun.xml.bind.v2.runtime.reflect.opt.Injector$1 (file:/storage/repos/ultimate/releaseScripts/default/UAutomizer-linux/plugins/com.sun.xml.bind_2.2.0.v201505121915.jar) to method java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int) WARNING: Please consider reporting this to the maintainers of com.sun.xml.bind.v2.runtime.reflect.opt.Injector$1 WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations WARNING: All illegal access operations will be denied in a future release Applying setting for plugin de.uni_freiburg.informatik.ultimate.plugins.generator.buchiautomizer: Fairness type for concurrent programs -> FAIRNESS_INTERSECTION [2023-09-08 14:42:16,533 INFO L75 nceAwareModelManager]: Repository-Root is: /tmp [2023-09-08 14:42:16,552 INFO L261 ainManager$Toolchain]: [Toolchain 1]: Applicable parser(s) successfully (re)initialized [2023-09-08 14:42:16,553 INFO L217 ainManager$Toolchain]: [Toolchain 1]: Toolchain selected. [2023-09-08 14:42:16,554 INFO L270 PluginConnector]: Initializing CDTParser... [2023-09-08 14:42:16,554 INFO L274 PluginConnector]: CDTParser initialized [2023-09-08 14:42:16,555 INFO L431 ainManager$Toolchain]: [Toolchain 1]: Parsing single file: /storage/repos/ultimate/releaseScripts/default/UAutomizer-linux/../../../trunk/examples/svcomp/weaver/chl-word-trans.wvr.c [2023-09-08 14:42:17,591 INFO L533 CDTParser]: Created temporary CDT project at NULL [2023-09-08 14:42:17,758 INFO L384 CDTParser]: Found 1 translation units. [2023-09-08 14:42:17,759 INFO L180 CDTParser]: Scanning /storage/repos/ultimate/trunk/examples/svcomp/weaver/chl-word-trans.wvr.c [2023-09-08 14:42:17,765 INFO L427 CDTParser]: About to delete temporary CDT project at /storage/repos/ultimate/releaseScripts/default/UAutomizer-linux/data/ebbaaedef/a86a7c7cea7448cdaac3da8d29655c05/FLAGdb5bfafdb [2023-09-08 14:42:17,777 INFO L435 CDTParser]: Successfully deleted /storage/repos/ultimate/releaseScripts/default/UAutomizer-linux/data/ebbaaedef/a86a7c7cea7448cdaac3da8d29655c05 [2023-09-08 14:42:17,779 INFO L299 ainManager$Toolchain]: ####################### [Toolchain 1] ####################### [2023-09-08 14:42:17,780 INFO L133 ToolchainWalker]: Walking toolchain with 5 elements. [2023-09-08 14:42:17,781 INFO L112 PluginConnector]: ------------------------CACSL2BoogieTranslator---------------------------- [2023-09-08 14:42:17,781 INFO L270 PluginConnector]: Initializing CACSL2BoogieTranslator... [2023-09-08 14:42:17,783 INFO L274 PluginConnector]: CACSL2BoogieTranslator initialized [2023-09-08 14:42:17,784 INFO L184 PluginConnector]: Executing the observer ACSLObjectContainerObserver from plugin CACSL2BoogieTranslator for "CDTParser AST 08.09 02:42:17" (1/1) ... [2023-09-08 14:42:17,785 INFO L204 PluginConnector]: Invalid model from CACSL2BoogieTranslator for observer de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator.ACSLObjectContainerObserver@3297e0cb and model type de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 08.09 02:42:17, skipping insertion in model container [2023-09-08 14:42:17,785 INFO L184 PluginConnector]: Executing the observer CACSL2BoogieTranslatorObserver from plugin CACSL2BoogieTranslator for "CDTParser AST 08.09 02:42:17" (1/1) ... [2023-09-08 14:42:17,790 INFO L145 MainTranslator]: Starting translation in SV-COMP mode [2023-09-08 14:42:17,813 INFO L178 MainTranslator]: Built tables and reachable declarations [2023-09-08 14:42:17,929 WARN L247 ndardFunctionHandler]: Function reach_error is already implemented but we override the implementation for the call at /storage/repos/ultimate/trunk/examples/svcomp/weaver/chl-word-trans.wvr.c[3292,3305] [2023-09-08 14:42:17,933 INFO L209 PostProcessor]: Analyzing one entry point: main [2023-09-08 14:42:17,941 INFO L203 MainTranslator]: Completed pre-run [2023-09-08 14:42:17,960 WARN L247 ndardFunctionHandler]: Function reach_error is already implemented but we override the implementation for the call at /storage/repos/ultimate/trunk/examples/svcomp/weaver/chl-word-trans.wvr.c[3292,3305] [2023-09-08 14:42:17,962 INFO L209 PostProcessor]: Analyzing one entry point: main [2023-09-08 14:42:17,975 INFO L208 MainTranslator]: Completed translation [2023-09-08 14:42:17,975 INFO L201 PluginConnector]: Adding new model de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 08.09 02:42:17 WrapperNode [2023-09-08 14:42:17,976 INFO L131 PluginConnector]: ------------------------ END CACSL2BoogieTranslator---------------------------- [2023-09-08 14:42:17,977 INFO L112 PluginConnector]: ------------------------Boogie Procedure Inliner---------------------------- [2023-09-08 14:42:17,977 INFO L270 PluginConnector]: Initializing Boogie Procedure Inliner... [2023-09-08 14:42:17,977 INFO L274 PluginConnector]: Boogie Procedure Inliner initialized [2023-09-08 14:42:17,982 INFO L184 PluginConnector]: Executing the observer TypeChecker from plugin Boogie Procedure Inliner for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 08.09 02:42:17" (1/1) ... [2023-09-08 14:42:17,988 INFO L184 PluginConnector]: Executing the observer Inliner from plugin Boogie Procedure Inliner for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 08.09 02:42:17" (1/1) ... [2023-09-08 14:42:18,008 INFO L138 Inliner]: procedures = 25, calls = 44, calls flagged for inlining = 8, calls inlined = 12, statements flattened = 172 [2023-09-08 14:42:18,008 INFO L131 PluginConnector]: ------------------------ END Boogie Procedure Inliner---------------------------- [2023-09-08 14:42:18,009 INFO L112 PluginConnector]: ------------------------Boogie Preprocessor---------------------------- [2023-09-08 14:42:18,009 INFO L270 PluginConnector]: Initializing Boogie Preprocessor... [2023-09-08 14:42:18,009 INFO L274 PluginConnector]: Boogie Preprocessor initialized [2023-09-08 14:42:18,015 INFO L184 PluginConnector]: Executing the observer EnsureBoogieModelObserver from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 08.09 02:42:17" (1/1) ... [2023-09-08 14:42:18,016 INFO L184 PluginConnector]: Executing the observer TypeChecker from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 08.09 02:42:17" (1/1) ... [2023-09-08 14:42:18,021 INFO L184 PluginConnector]: Executing the observer ConstExpander from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 08.09 02:42:17" (1/1) ... [2023-09-08 14:42:18,022 INFO L184 PluginConnector]: Executing the observer StructExpander from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 08.09 02:42:17" (1/1) ... [2023-09-08 14:42:18,028 INFO L184 PluginConnector]: Executing the observer UnstructureCode from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 08.09 02:42:17" (1/1) ... [2023-09-08 14:42:18,032 INFO L184 PluginConnector]: Executing the observer FunctionInliner from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 08.09 02:42:17" (1/1) ... [2023-09-08 14:42:18,033 INFO L184 PluginConnector]: Executing the observer LTLStepAnnotator from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 08.09 02:42:17" (1/1) ... [2023-09-08 14:42:18,034 INFO L184 PluginConnector]: Executing the observer BoogieSymbolTableConstructor from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 08.09 02:42:17" (1/1) ... [2023-09-08 14:42:18,037 INFO L131 PluginConnector]: ------------------------ END Boogie Preprocessor---------------------------- [2023-09-08 14:42:18,037 INFO L112 PluginConnector]: ------------------------RCFGBuilder---------------------------- [2023-09-08 14:42:18,038 INFO L270 PluginConnector]: Initializing RCFGBuilder... [2023-09-08 14:42:18,038 INFO L274 PluginConnector]: RCFGBuilder initialized [2023-09-08 14:42:18,038 INFO L184 PluginConnector]: Executing the observer RCFGBuilderObserver from plugin RCFGBuilder for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 08.09 02:42:17" (1/1) ... [2023-09-08 14:42:18,043 INFO L173 SolverBuilder]: Constructing external solver with command: z3 SMTLIB2_COMPLIANT=true -memory:1024 -smt2 -in -t:12000 [2023-09-08 14:42:18,058 INFO L189 MonitoredProcess]: No working directory specified, using /storage/repos/ultimate/releaseScripts/default/UAutomizer-linux/z3 [2023-09-08 14:42:18,072 INFO L229 MonitoredProcess]: Starting monitored process 1 with /storage/repos/ultimate/releaseScripts/default/UAutomizer-linux/z3 SMTLIB2_COMPLIANT=true -memory:1024 -smt2 -in -t:12000 (exit command is (exit), workingDir is null) [2023-09-08 14:42:18,079 INFO L327 MonitoredProcess]: [MP /storage/repos/ultimate/releaseScripts/default/UAutomizer-linux/z3 SMTLIB2_COMPLIANT=true -memory:1024 -smt2 -in -t:12000 (1)] Waiting until timeout for monitored process [2023-09-08 14:42:18,108 INFO L130 BoogieDeclarations]: Found specification of procedure #Ultimate.allocInit [2023-09-08 14:42:18,108 INFO L130 BoogieDeclarations]: Found specification of procedure #Ultimate.allocOnStack [2023-09-08 14:42:18,108 INFO L130 BoogieDeclarations]: Found specification of procedure write~int [2023-09-08 14:42:18,108 INFO L130 BoogieDeclarations]: Found specification of procedure read~int [2023-09-08 14:42:18,108 INFO L130 BoogieDeclarations]: Found specification of procedure thread1 [2023-09-08 14:42:18,108 INFO L138 BoogieDeclarations]: Found implementation of procedure thread1 [2023-09-08 14:42:18,108 INFO L130 BoogieDeclarations]: Found specification of procedure thread2 [2023-09-08 14:42:18,108 INFO L138 BoogieDeclarations]: Found implementation of procedure thread2 [2023-09-08 14:42:18,109 INFO L130 BoogieDeclarations]: Found specification of procedure thread3 [2023-09-08 14:42:18,109 INFO L138 BoogieDeclarations]: Found implementation of procedure thread3 [2023-09-08 14:42:18,109 INFO L130 BoogieDeclarations]: Found specification of procedure write~init~int [2023-09-08 14:42:18,109 INFO L130 BoogieDeclarations]: Found specification of procedure #Ultimate.allocOnHeap [2023-09-08 14:42:18,109 INFO L130 BoogieDeclarations]: Found specification of procedure ULTIMATE.start [2023-09-08 14:42:18,109 INFO L138 BoogieDeclarations]: Found implementation of procedure ULTIMATE.start [2023-09-08 14:42:18,109 INFO L130 BoogieDeclarations]: Found specification of procedure ULTIMATE.dealloc [2023-09-08 14:42:18,110 WARN L210 CfgBuilder]: User set CodeBlockSize to SequenceOfStatements but program contains fork statements. Overwriting the user preferences and setting CodeBlockSize to OneNontrivialStatement [2023-09-08 14:42:18,205 INFO L236 CfgBuilder]: Building ICFG [2023-09-08 14:42:18,206 INFO L262 CfgBuilder]: Building CFG for each procedure with an implementation [2023-09-08 14:42:18,551 INFO L277 CfgBuilder]: Performing block encoding [2023-09-08 14:42:18,586 INFO L297 CfgBuilder]: Using the 1 location(s) as analysis (start of procedure ULTIMATE.start) [2023-09-08 14:42:18,586 INFO L302 CfgBuilder]: Removed 6 assume(true) statements. [2023-09-08 14:42:18,589 INFO L201 PluginConnector]: Adding new model de.uni_freiburg.informatik.ultimate.plugins.generator.rcfgbuilder CFG 08.09 02:42:18 BoogieIcfgContainer [2023-09-08 14:42:18,589 INFO L131 PluginConnector]: ------------------------ END RCFGBuilder---------------------------- [2023-09-08 14:42:18,590 INFO L112 PluginConnector]: ------------------------BuchiAutomizer---------------------------- [2023-09-08 14:42:18,590 INFO L270 PluginConnector]: Initializing BuchiAutomizer... [2023-09-08 14:42:18,592 INFO L274 PluginConnector]: BuchiAutomizer initialized [2023-09-08 14:42:18,593 INFO L99 BuchiAutomizer]: Safety of program was proven or not checked, starting termination analysis [2023-09-08 14:42:18,593 INFO L184 PluginConnector]: Executing the observer BuchiAutomizerObserver from plugin BuchiAutomizer for "CDTParser AST 08.09 02:42:17" (1/3) ... [2023-09-08 14:42:18,594 INFO L204 PluginConnector]: Invalid model from BuchiAutomizer for observer de.uni_freiburg.informatik.ultimate.plugins.generator.buchiautomizer.BuchiAutomizerObserver@63a79c2a and model type de.uni_freiburg.informatik.ultimate.plugins.generator.buchiautomizer AST 08.09 02:42:18, skipping insertion in model container [2023-09-08 14:42:18,594 INFO L99 BuchiAutomizer]: Safety of program was proven or not checked, starting termination analysis [2023-09-08 14:42:18,594 INFO L184 PluginConnector]: Executing the observer BuchiAutomizerObserver from plugin BuchiAutomizer for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 08.09 02:42:17" (2/3) ... [2023-09-08 14:42:18,594 INFO L204 PluginConnector]: Invalid model from BuchiAutomizer for observer de.uni_freiburg.informatik.ultimate.plugins.generator.buchiautomizer.BuchiAutomizerObserver@63a79c2a and model type de.uni_freiburg.informatik.ultimate.plugins.generator.buchiautomizer AST 08.09 02:42:18, skipping insertion in model container [2023-09-08 14:42:18,594 INFO L99 BuchiAutomizer]: Safety of program was proven or not checked, starting termination analysis [2023-09-08 14:42:18,594 INFO L184 PluginConnector]: Executing the observer BuchiAutomizerObserver from plugin BuchiAutomizer for "de.uni_freiburg.informatik.ultimate.plugins.generator.rcfgbuilder CFG 08.09 02:42:18" (3/3) ... [2023-09-08 14:42:18,595 INFO L332 chiAutomizerObserver]: Analyzing ICFG chl-word-trans.wvr.c [2023-09-08 14:42:18,694 INFO L144 ThreadInstanceAdder]: Constructed 3 joinOtherThreadTransitions. [2023-09-08 14:42:18,727 INFO L73 FinitePrefix]: Start finitePrefix. Operand has 262 places, 283 transitions, 590 flow [2023-09-08 14:42:18,834 INFO L124 PetriNetUnfolderBase]: 28/277 cut-off events. [2023-09-08 14:42:18,835 INFO L125 PetriNetUnfolderBase]: For 3/3 co-relation queries the response was YES. [2023-09-08 14:42:18,842 INFO L83 FinitePrefix]: Finished finitePrefix Result has 290 conditions, 277 events. 28/277 cut-off events. For 3/3 co-relation queries the response was YES. Maximal size of possible extension queue 6. Compared 366 event pairs, 0 based on Foata normal form. 0/249 useless extension candidates. Maximal degree in co-relation 223. Up to 3 conditions per place. [2023-09-08 14:42:18,843 INFO L82 GeneralOperation]: Start removeDead. Operand has 262 places, 283 transitions, 590 flow [2023-09-08 14:42:18,856 INFO L88 GeneralOperation]: Finished RemoveDead, result has has 259 places, 277 transitions, 572 flow [2023-09-08 14:42:18,869 INFO L303 stractBuchiCegarLoop]: Interprodecural is true [2023-09-08 14:42:18,869 INFO L304 stractBuchiCegarLoop]: Hoare is false [2023-09-08 14:42:18,869 INFO L305 stractBuchiCegarLoop]: Compute interpolants for ForwardPredicates [2023-09-08 14:42:18,869 INFO L306 stractBuchiCegarLoop]: Backedges is STRAIGHT_LINE [2023-09-08 14:42:18,869 INFO L307 stractBuchiCegarLoop]: Determinization is PREDICATE_ABSTRACTION [2023-09-08 14:42:18,870 INFO L308 stractBuchiCegarLoop]: Difference is false [2023-09-08 14:42:18,870 INFO L309 stractBuchiCegarLoop]: Minimize is MINIMIZE_SEVPA [2023-09-08 14:42:18,870 INFO L313 stractBuchiCegarLoop]: ======== Iteration 0 == of CEGAR loop == BuchiAutomatonCegarLoop ======== [2023-09-08 14:42:18,871 INFO L72 BuchiIsEmpty]: Start buchiIsEmpty. Operand null [2023-09-08 14:43:35,123 INFO L131 ngComponentsAnalysis]: Automaton has 3 accepting balls. 21 [2023-09-08 14:43:35,123 INFO L87 BuchiIsEmpty]: Finished buchiIsEmpty Result is false [2023-09-08 14:43:35,123 INFO L119 BuchiIsEmpty]: Starting construction of run [2023-09-08 14:43:35,134 INFO L148 hiAutomatonCegarLoop]: Counterexample stem histogram [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1] [2023-09-08 14:43:35,134 INFO L149 hiAutomatonCegarLoop]: Counterexample loop histogram [1, 1, 1, 1, 1, 1, 1] [2023-09-08 14:43:35,134 INFO L335 stractBuchiCegarLoop]: ======== Iteration 1 ============ [2023-09-08 14:43:35,135 INFO L72 BuchiIsEmpty]: Start buchiIsEmpty. Operand null