currentdate: 0
registration cancelled: patron-id 123456 already exists
checkin cancelled: book L123.2 V2 is not checked out
L123.1 V1	Rubini	Linux Device Drivers
L123.2 V2	Bach	Linux Kernel Internals
N090.2 V3	Tannenbaum	High Speed Networking
K23.2 V4: call number doesnt exist
Out: L123.1 V1, Rubini, Linux Device Drivers. Due data: 7
currentdate: 8
123456, Stephen. patron-id has books overdue. Checkout cancelled.
Available: L123.2 V2, Bach, Linux Kernel Internals
N090.2 V3, Tannenbaum, High Speed Networking.