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 customer_master_index (master_customer_id VARCHAR, cmi_details VARCHAR)
TABLE: CREATE TABLE cmi_cross_references (source_system_code VARCHAR, master_customer_id VARCHAR)

### Question ###
What are the distinct cross reference source system codes which are related to the master customer details 'Gottlieb, Becker and Wyman'?

### Accurate SQL ###

SELECT DISTINCT T2.source_system_code FROM customer_master_index AS T1 JOIN cmi_cross_references AS T2 ON T1.master_customer_id = T2.master_customer_id WHERE T1.cmi_details = 'Gottlieb ,  Becker and Wyman'