Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_15970 ( "Formula" text, "Notation" text, "T c (K)" real, "No. of Cu-O planes in unit cell" real, "Crystal structure" text )

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

### Accurate SQL ###

SELECT "Notation" FROM table_15970 WHERE "Crystal structure" = 'Tetragonal' AND "Formula" = 'Bi 2 Sr 2 CaCu 2 O 8'