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_50559 ( "Name" text, "Year Began" text, "Registration" text, "Userpics Free" text, "Userpics Paid" text, "Monthly Cost for Paid Account" text, "Yearly Cost for Paid Account" text, "Permanent Account" text )

### Question ###
Which permanent account has registration of invite-only and userpics free of unknown?

### Accurate SQL ###

SELECT "Permanent Account" FROM table_50559 WHERE "Userpics Free" = 'unknown' AND "Registration" = 'invite-only'