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_15972 ( "Formula" text, "Notation" text, "T c (K)" real, "No. of Cu-O planes in unit cell" real, "Crystal structure" text )

### Question ###
What is the crystal structure for the formula yba 2 cu 3 o 7?

### Accurate SQL ###

SELECT "Crystal structure" FROM table_15972 WHERE "Formula" = 'YBa 2 Cu 3 O 7'