Parsed test spec with 4 sessions

starting permutation: s1a s2a s2b s3a s4a s1b s1c s2c s3c s4c
step s1a: LOCK TABLE a1 IN SHARE UPDATE EXCLUSIVE MODE;
step s2a: LOCK TABLE a2 IN ACCESS SHARE MODE;
step s2b: LOCK TABLE a1 IN SHARE UPDATE EXCLUSIVE MODE; <waiting ...>
step s3a: LOCK TABLE a2 IN ACCESS EXCLUSIVE MODE; <waiting ...>
step s4a: LOCK TABLE a2 IN ACCESS EXCLUSIVE MODE; <waiting ...>
step s1b: LOCK TABLE a2 IN SHARE UPDATE EXCLUSIVE MODE; <waiting ...>
step s1b: <... completed>
step s1c: COMMIT;
step s2b: <... completed>
step s2c: COMMIT;
step s3a: <... completed>
step s3c: COMMIT;
step s4a: <... completed>
step s4c: COMMIT;