Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
What is the notion when the crystal structure is tetragonal and the formula is bi 2 sr 2 cacu 2 o 8

### Inputs:
table_name: table, columns: ['Formula', 'Notation', 'T c (K)', 'No. of Cu-O planes in unit cell', 'Crystal structure']

### Response:
SELECT Notation FROM table WHERE Crystal structure = Tetragonal AND Formula = Bi 2 Sr 2 CaCu 2 O 8