user: Question: What is the Nat with a Mutual consent Loan return and has a Free transfer fee?
Columns: ['Nat.', 'Name', 'Moving to', 'Type', 'Transfer window', 'Transfer fee', 'Source']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['GRE', 'Machlas', 'Retired', 'Retirement', 'Summer', '—', 'contra.gr']
SQL:

assistant: SELECT "Nat." FROM "Table" WHERE "Transfer fee" = 'Free' AND "Type" = 'Mutual consent Loan return';