Table schema:
CREATE TABLE customer_master_index (master_customer_id VARCHAR, cmi_details VARCHAR); 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'?
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'