/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_LAZY -i ../../../trunk/examples/svcomp/weaver/parallel-parallel-sum-2.wvr.c -------------------------------------------------------------------------------- This is Ultimate 0.2.3-wip.me.fairness-42053ae-m [2023-09-17 12:01:12,078 INFO L172 SettingsManager]: Resetting all preferences to default values... [2023-09-17 12:01:12,152 INFO L100 SettingsManager]: Loading settings from /storage/repos/ultimate/releaseScripts/default/UAutomizer-linux/../../../trunk/examples/settings/default/automizer/svcomp-Termination-32bit-Automizer_Default.epf [2023-09-17 12:01:12,181 INFO L114 SettingsManager]: Preferences different from defaults after loading the file: [2023-09-17 12:01:12,181 INFO L135 SettingsManager]: Preferences of UltimateCore differ from their defaults: [2023-09-17 12:01:12,181 INFO L137 SettingsManager]: * Log level for class=de.uni_freiburg.informatik.ultimate.lib.smtlibutils.quantifier.QuantifierPusher=ERROR; [2023-09-17 12:01:12,182 INFO L135 SettingsManager]: Preferences of BlockEncodingV2 differ from their defaults: [2023-09-17 12:01:12,182 INFO L137 SettingsManager]: * Create parallel compositions if possible=false [2023-09-17 12:01:12,183 INFO L137 SettingsManager]: * Use SBE=true [2023-09-17 12:01:12,183 INFO L135 SettingsManager]: Preferences of BuchiAutomizer differ from their defaults: [2023-09-17 12:01:12,183 INFO L137 SettingsManager]: * NCSB implementation=INTSET_LAZY3 [2023-09-17 12:01:12,184 INFO L137 SettingsManager]: * Use old map elimination=false [2023-09-17 12:01:12,184 INFO L137 SettingsManager]: * Use external solver (rank synthesis)=false [2023-09-17 12:01:12,184 INFO L137 SettingsManager]: * Use only trivial implications for array writes=true [2023-09-17 12:01:12,184 INFO L137 SettingsManager]: * Rank analysis=LINEAR_WITH_GUESSES [2023-09-17 12:01:12,185 INFO L135 SettingsManager]: Preferences of CACSL2BoogieTranslator differ from their defaults: [2023-09-17 12:01:12,185 INFO L137 SettingsManager]: * sizeof long=4 [2023-09-17 12:01:12,185 INFO L137 SettingsManager]: * Check unreachability of error function in SV-COMP mode=false [2023-09-17 12:01:12,185 INFO L137 SettingsManager]: * Overapproximate operations on floating types=true [2023-09-17 12:01:12,185 INFO L137 SettingsManager]: * sizeof POINTER=4 [2023-09-17 12:01:12,186 INFO L137 SettingsManager]: * Check division by zero=IGNORE [2023-09-17 12:01:12,191 INFO L137 SettingsManager]: * Pointer to allocated memory at dereference=ASSUME [2023-09-17 12:01:12,191 INFO L137 SettingsManager]: * If two pointers are subtracted or compared they have the same base address=ASSUME [2023-09-17 12:01:12,191 INFO L137 SettingsManager]: * Check array bounds for arrays that are off heap=ASSUME [2023-09-17 12:01:12,194 INFO L137 SettingsManager]: * sizeof long double=12 [2023-09-17 12:01:12,195 INFO L137 SettingsManager]: * Check if freed pointer was valid=false [2023-09-17 12:01:12,195 INFO L137 SettingsManager]: * Assume nondeterminstic values are in range=false [2023-09-17 12:01:12,195 INFO L137 SettingsManager]: * Use constant arrays=true [2023-09-17 12:01:12,196 INFO L137 SettingsManager]: * Pointer base address is valid at dereference=ASSUME [2023-09-17 12:01:12,196 INFO L135 SettingsManager]: Preferences of RCFGBuilder differ from their defaults: [2023-09-17 12:01:12,197 INFO L137 SettingsManager]: * Size of a code block=SequenceOfStatements [2023-09-17 12:01:12,197 INFO L135 SettingsManager]: Preferences of TraceAbstraction differ from their defaults: [2023-09-17 12:01:12,197 INFO L137 SettingsManager]: * Trace refinement strategy=CAMEL [2023-09-17 12:01:12,197 INFO L137 SettingsManager]: * Apply one-shot large block encoding in concurrent analysis=false [2023-09-17 12:01:12,198 INFO L135 SettingsManager]: Preferences of IcfgTransformer differ from their defaults: [2023-09-17 12:01:12,198 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$1 WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations WARNING: All illegal access operations will be denied in a future release Applying setting for plugin de.uni_freiburg.informatik.ultimate.plugins.generator.buchiautomizer: Fairness type for concurrent programs -> FAIRNESS_LAZY [2023-09-17 12:01:12,391 INFO L75 nceAwareModelManager]: Repository-Root is: /tmp [2023-09-17 12:01:12,413 INFO L261 ainManager$Toolchain]: [Toolchain 1]: Applicable parser(s) successfully (re)initialized [2023-09-17 12:01:12,415 INFO L217 ainManager$Toolchain]: [Toolchain 1]: Toolchain selected. [2023-09-17 12:01:12,416 INFO L270 PluginConnector]: Initializing CDTParser... [2023-09-17 12:01:12,416 INFO L274 PluginConnector]: CDTParser initialized [2023-09-17 12:01:12,418 INFO L431 ainManager$Toolchain]: [Toolchain 1]: Parsing single file: /storage/repos/ultimate/releaseScripts/default/UAutomizer-linux/../../../trunk/examples/svcomp/weaver/parallel-parallel-sum-2.wvr.c [2023-09-17 12:01:13,540 INFO L533 CDTParser]: Created temporary CDT project at NULL [2023-09-17 12:01:13,905 INFO L384 CDTParser]: Found 1 translation units. [2023-09-17 12:01:13,906 INFO L180 CDTParser]: Scanning /storage/repos/ultimate/trunk/examples/svcomp/weaver/parallel-parallel-sum-2.wvr.c [2023-09-17 12:01:13,916 INFO L427 CDTParser]: About to delete temporary CDT project at /storage/repos/ultimate/releaseScripts/default/UAutomizer-linux/data/853976290/38ddc9b5ba994415a8d943182177ea85/FLAG46b0147cb [2023-09-17 12:01:13,937 INFO L435 CDTParser]: Successfully deleted /storage/repos/ultimate/releaseScripts/default/UAutomizer-linux/data/853976290/38ddc9b5ba994415a8d943182177ea85 [2023-09-17 12:01:13,940 INFO L299 ainManager$Toolchain]: ####################### [Toolchain 1] ####################### [2023-09-17 12:01:13,942 INFO L133 ToolchainWalker]: Walking toolchain with 5 elements. [2023-09-17 12:01:13,966 INFO L112 PluginConnector]: ------------------------CACSL2BoogieTranslator---------------------------- [2023-09-17 12:01:13,966 INFO L270 PluginConnector]: Initializing CACSL2BoogieTranslator... [2023-09-17 12:01:13,976 INFO L274 PluginConnector]: CACSL2BoogieTranslator initialized [2023-09-17 12:01:13,978 INFO L184 PluginConnector]: Executing the observer ACSLObjectContainerObserver from plugin CACSL2BoogieTranslator for "CDTParser AST 17.09 12:01:13" (1/1) ... [2023-09-17 12:01:13,979 INFO L204 PluginConnector]: Invalid model from CACSL2BoogieTranslator for observer de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator.ACSLObjectContainerObserver@509b1652 and model type de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 17.09 12:01:13, skipping insertion in model container [2023-09-17 12:01:13,979 INFO L184 PluginConnector]: Executing the observer CACSL2BoogieTranslatorObserver from plugin CACSL2BoogieTranslator for "CDTParser AST 17.09 12:01:13" (1/1) ... [2023-09-17 12:01:13,995 INFO L145 MainTranslator]: Starting translation in SV-COMP mode [2023-09-17 12:01:14,030 INFO L178 MainTranslator]: Built tables and reachable declarations [2023-09-17 12:01:14,162 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/parallel-parallel-sum-2.wvr.c[4087,4100] [2023-09-17 12:01:14,166 INFO L209 PostProcessor]: Analyzing one entry point: main [2023-09-17 12:01:14,174 INFO L203 MainTranslator]: Completed pre-run [2023-09-17 12:01:14,191 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/parallel-parallel-sum-2.wvr.c[4087,4100] [2023-09-17 12:01:14,193 INFO L209 PostProcessor]: Analyzing one entry point: main [2023-09-17 12:01:14,199 WARN L667 CHandler]: The function __VERIFIER_atomic_begin is called, but not defined or handled by StandardFunctionHandler. [2023-09-17 12:01:14,199 WARN L667 CHandler]: The function __VERIFIER_atomic_end is called, but not defined or handled by StandardFunctionHandler. [2023-09-17 12:01:14,204 INFO L208 MainTranslator]: Completed translation [2023-09-17 12:01:14,204 INFO L201 PluginConnector]: Adding new model de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 17.09 12:01:14 WrapperNode [2023-09-17 12:01:14,204 INFO L131 PluginConnector]: ------------------------ END CACSL2BoogieTranslator---------------------------- [2023-09-17 12:01:14,205 INFO L112 PluginConnector]: ------------------------Boogie Procedure Inliner---------------------------- [2023-09-17 12:01:14,205 INFO L270 PluginConnector]: Initializing Boogie Procedure Inliner... [2023-09-17 12:01:14,205 INFO L274 PluginConnector]: Boogie Procedure Inliner initialized [2023-09-17 12:01:14,210 INFO L184 PluginConnector]: Executing the observer TypeChecker from plugin Boogie Procedure Inliner for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 17.09 12:01:14" (1/1) ... [2023-09-17 12:01:14,216 INFO L184 PluginConnector]: Executing the observer Inliner from plugin Boogie Procedure Inliner for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 17.09 12:01:14" (1/1) ... [2023-09-17 12:01:14,237 INFO L138 Inliner]: procedures = 29, calls = 82, calls flagged for inlining = 22, calls inlined = 32, statements flattened = 366 [2023-09-17 12:01:14,238 INFO L131 PluginConnector]: ------------------------ END Boogie Procedure Inliner---------------------------- [2023-09-17 12:01:14,239 INFO L112 PluginConnector]: ------------------------Boogie Preprocessor---------------------------- [2023-09-17 12:01:14,239 INFO L270 PluginConnector]: Initializing Boogie Preprocessor... [2023-09-17 12:01:14,239 INFO L274 PluginConnector]: Boogie Preprocessor initialized [2023-09-17 12:01:14,246 INFO L184 PluginConnector]: Executing the observer EnsureBoogieModelObserver from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 17.09 12:01:14" (1/1) ... [2023-09-17 12:01:14,246 INFO L184 PluginConnector]: Executing the observer TypeChecker from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 17.09 12:01:14" (1/1) ... [2023-09-17 12:01:14,250 INFO L184 PluginConnector]: Executing the observer ConstExpander from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 17.09 12:01:14" (1/1) ... [2023-09-17 12:01:14,250 INFO L184 PluginConnector]: Executing the observer StructExpander from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 17.09 12:01:14" (1/1) ... [2023-09-17 12:01:14,257 INFO L184 PluginConnector]: Executing the observer UnstructureCode from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 17.09 12:01:14" (1/1) ... [2023-09-17 12:01:14,260 INFO L184 PluginConnector]: Executing the observer FunctionInliner from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 17.09 12:01:14" (1/1) ... [2023-09-17 12:01:14,262 INFO L184 PluginConnector]: Executing the observer LTLStepAnnotator from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 17.09 12:01:14" (1/1) ... [2023-09-17 12:01:14,263 INFO L184 PluginConnector]: Executing the observer BoogieSymbolTableConstructor from plugin Boogie Preprocessor for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 17.09 12:01:14" (1/1) ... [2023-09-17 12:01:14,266 INFO L131 PluginConnector]: ------------------------ END Boogie Preprocessor---------------------------- [2023-09-17 12:01:14,267 INFO L112 PluginConnector]: ------------------------RCFGBuilder---------------------------- [2023-09-17 12:01:14,267 INFO L270 PluginConnector]: Initializing RCFGBuilder... [2023-09-17 12:01:14,267 INFO L274 PluginConnector]: RCFGBuilder initialized [2023-09-17 12:01:14,267 INFO L184 PluginConnector]: Executing the observer RCFGBuilderObserver from plugin RCFGBuilder for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 17.09 12:01:14" (1/1) ... [2023-09-17 12:01:14,272 INFO L173 SolverBuilder]: Constructing external solver with command: z3 SMTLIB2_COMPLIANT=true -memory:1024 -smt2 -in -t:12000 [2023-09-17 12:01:14,281 INFO L189 MonitoredProcess]: No working directory specified, using /storage/repos/ultimate/releaseScripts/default/UAutomizer-linux/z3 [2023-09-17 12:01:14,291 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) [2023-09-17 12:01:14,294 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 [2023-09-17 12:01:14,324 INFO L130 BoogieDeclarations]: Found specification of procedure #Ultimate.allocInit [2023-09-17 12:01:14,325 INFO L130 BoogieDeclarations]: Found specification of procedure #Ultimate.allocOnStack [2023-09-17 12:01:14,325 INFO L130 BoogieDeclarations]: Found specification of procedure write~int [2023-09-17 12:01:14,325 INFO L130 BoogieDeclarations]: Found specification of procedure read~int [2023-09-17 12:01:14,325 INFO L130 BoogieDeclarations]: Found specification of procedure thread1 [2023-09-17 12:01:14,325 INFO L138 BoogieDeclarations]: Found implementation of procedure thread1 [2023-09-17 12:01:14,325 INFO L130 BoogieDeclarations]: Found specification of procedure thread2 [2023-09-17 12:01:14,325 INFO L138 BoogieDeclarations]: Found implementation of procedure thread2 [2023-09-17 12:01:14,325 INFO L130 BoogieDeclarations]: Found specification of procedure thread3 [2023-09-17 12:01:14,325 INFO L138 BoogieDeclarations]: Found implementation of procedure thread3 [2023-09-17 12:01:14,325 INFO L130 BoogieDeclarations]: Found specification of procedure thread4 [2023-09-17 12:01:14,325 INFO L138 BoogieDeclarations]: Found implementation of procedure thread4 [2023-09-17 12:01:14,326 INFO L130 BoogieDeclarations]: Found specification of procedure write~init~int [2023-09-17 12:01:14,326 INFO L130 BoogieDeclarations]: Found specification of procedure thread5 [2023-09-17 12:01:14,326 INFO L138 BoogieDeclarations]: Found implementation of procedure thread5 [2023-09-17 12:01:14,326 INFO L130 BoogieDeclarations]: Found specification of procedure thread6 [2023-09-17 12:01:14,326 INFO L138 BoogieDeclarations]: Found implementation of procedure thread6 [2023-09-17 12:01:14,326 INFO L130 BoogieDeclarations]: Found specification of procedure __VERIFIER_atomic_end [2023-09-17 12:01:14,326 INFO L130 BoogieDeclarations]: Found specification of procedure __VERIFIER_atomic_begin [2023-09-17 12:01:14,326 INFO L130 BoogieDeclarations]: Found specification of procedure #Ultimate.allocOnHeap [2023-09-17 12:01:14,326 INFO L130 BoogieDeclarations]: Found specification of procedure ULTIMATE.start [2023-09-17 12:01:14,326 INFO L138 BoogieDeclarations]: Found implementation of procedure ULTIMATE.start [2023-09-17 12:01:14,326 INFO L130 BoogieDeclarations]: Found specification of procedure ULTIMATE.dealloc [2023-09-17 12:01:14,328 WARN L210 CfgBuilder]: User set CodeBlockSize to SequenceOfStatements but program contains fork statements. Overwriting the user preferences and setting CodeBlockSize to OneNontrivialStatement [2023-09-17 12:01:14,429 INFO L236 CfgBuilder]: Building ICFG [2023-09-17 12:01:14,431 INFO L262 CfgBuilder]: Building CFG for each procedure with an implementation [2023-09-17 12:01:14,775 INFO L277 CfgBuilder]: Performing block encoding [2023-09-17 12:01:15,002 INFO L297 CfgBuilder]: Using the 1 location(s) as analysis (start of procedure ULTIMATE.start) [2023-09-17 12:01:15,003 INFO L302 CfgBuilder]: Removed 5 assume(true) statements. [2023-09-17 12:01:15,006 INFO L201 PluginConnector]: Adding new model de.uni_freiburg.informatik.ultimate.plugins.generator.rcfgbuilder CFG 17.09 12:01:15 BoogieIcfgContainer [2023-09-17 12:01:15,006 INFO L131 PluginConnector]: ------------------------ END RCFGBuilder---------------------------- [2023-09-17 12:01:15,007 INFO L112 PluginConnector]: ------------------------BuchiAutomizer---------------------------- [2023-09-17 12:01:15,008 INFO L270 PluginConnector]: Initializing BuchiAutomizer... [2023-09-17 12:01:15,011 INFO L274 PluginConnector]: BuchiAutomizer initialized [2023-09-17 12:01:15,012 INFO L99 BuchiAutomizer]: Safety of program was proven or not checked, starting termination analysis [2023-09-17 12:01:15,013 INFO L184 PluginConnector]: Executing the observer BuchiAutomizerObserver from plugin BuchiAutomizer for "CDTParser AST 17.09 12:01:13" (1/3) ... [2023-09-17 12:01:15,014 INFO L204 PluginConnector]: Invalid model from BuchiAutomizer for observer de.uni_freiburg.informatik.ultimate.plugins.generator.buchiautomizer.BuchiAutomizerObserver@51ad1a5e and model type de.uni_freiburg.informatik.ultimate.plugins.generator.buchiautomizer AST 17.09 12:01:15, skipping insertion in model container [2023-09-17 12:01:15,014 INFO L99 BuchiAutomizer]: Safety of program was proven or not checked, starting termination analysis [2023-09-17 12:01:15,014 INFO L184 PluginConnector]: Executing the observer BuchiAutomizerObserver from plugin BuchiAutomizer for "de.uni_freiburg.informatik.ultimate.plugins.generator.cacsl2boogietranslator AST 17.09 12:01:14" (2/3) ... [2023-09-17 12:01:15,014 INFO L204 PluginConnector]: Invalid model from BuchiAutomizer for observer de.uni_freiburg.informatik.ultimate.plugins.generator.buchiautomizer.BuchiAutomizerObserver@51ad1a5e and model type de.uni_freiburg.informatik.ultimate.plugins.generator.buchiautomizer AST 17.09 12:01:15, skipping insertion in model container [2023-09-17 12:01:15,014 INFO L99 BuchiAutomizer]: Safety of program was proven or not checked, starting termination analysis [2023-09-17 12:01:15,014 INFO L184 PluginConnector]: Executing the observer BuchiAutomizerObserver from plugin BuchiAutomizer for "de.uni_freiburg.informatik.ultimate.plugins.generator.rcfgbuilder CFG 17.09 12:01:15" (3/3) ... [2023-09-17 12:01:15,016 INFO L332 chiAutomizerObserver]: Analyzing ICFG parallel-parallel-sum-2.wvr.c [2023-09-17 12:01:15,154 INFO L144 ThreadInstanceAdder]: Constructed 0 joinOtherThreadTransitions. [2023-09-17 12:01:15,192 INFO L73 FinitePrefix]: Start finitePrefix. Operand has 237 places, 241 transitions, 512 flow [2023-09-17 12:01:15,317 INFO L124 PetriNetUnfolderBase]: 17/229 cut-off events. [2023-09-17 12:01:15,317 INFO L125 PetriNetUnfolderBase]: For 0/0 co-relation queries the response was YES. [2023-09-17 12:01:15,344 INFO L83 FinitePrefix]: Finished finitePrefix Result has 248 conditions, 229 events. 17/229 cut-off events. For 0/0 co-relation queries the response was YES. Maximal size of possible extension queue 9. Compared 359 event pairs, 0 based on Foata normal form. 0/212 useless extension candidates. Maximal degree in co-relation 212. Up to 2 conditions per place. [2023-09-17 12:01:15,345 INFO L82 GeneralOperation]: Start removeDead. Operand has 237 places, 241 transitions, 512 flow [2023-09-17 12:01:15,380 INFO L88 GeneralOperation]: Finished RemoveDead, result has has 231 places, 229 transitions, 476 flow [2023-09-17 12:01:15,399 INFO L303 stractBuchiCegarLoop]: Interprodecural is true [2023-09-17 12:01:15,400 INFO L304 stractBuchiCegarLoop]: Hoare is false [2023-09-17 12:01:15,400 INFO L305 stractBuchiCegarLoop]: Compute interpolants for ForwardPredicates [2023-09-17 12:01:15,400 INFO L306 stractBuchiCegarLoop]: Backedges is STRAIGHT_LINE [2023-09-17 12:01:15,400 INFO L307 stractBuchiCegarLoop]: Determinization is PREDICATE_ABSTRACTION [2023-09-17 12:01:15,400 INFO L308 stractBuchiCegarLoop]: Difference is false [2023-09-17 12:01:15,400 INFO L309 stractBuchiCegarLoop]: Minimize is MINIMIZE_SEVPA [2023-09-17 12:01:15,401 INFO L313 stractBuchiCegarLoop]: ======== Iteration 0 == of CEGAR loop == BuchiAutomatonCegarLoop ======== [2023-09-17 12:01:15,403 INFO L72 BuchiIsEmpty]: Start buchiIsEmpty. Operand null