Relational algebra problem

Have a relational database with the following tables

RESTAURANT(RT_ID, NAME, TYPE, LOCATION)
PROXIMITY(RT1_ID, RT2_ID, DISTANCE)
USER(U_ID, NAME, EMAIL)
REVIEW(U_ID, RT_ID, RT_DATE, RATING, COMMENT)

What’s the relational algebra for “name of any user who has never given Chez Brian a rating lower than 5”?

$\Pi _{NAME} (USER) - \Pi _{NAME} ( \sigma _{RESTNAME='Chez\ Brian' \wedge RATING < 5}( \rho (RESTAURANT(NAME \rightarrow RESTNAME), RESTAURANT) \Join REVIEW) \Join USER)$

Is this right?

CoSQL: SQL and noSQL are really just two sides of the same coin (cacm.acm.org)

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