# Restriction¶

## Restriction operators & and -¶

The restriction operator A & cond selects the subset of relation A that meet the condition cond. Its negated counterpart A - cond selects the subset of relation A that does not meet the condition cond.

The condition cond may be one of the following:

• another relation,
• a mapping (e.g. dict in Python or struct in MATLAB).
• an expression in a character string.
• a collection of conditions (e.g. a list in Python or a cell array in MATLAB)
• an AndList
• A boolean expression (True or False in Python or true or false in MATLAB)

### Restriction with a relation¶

When restricting relation A with another relation A & B, the two relations must be join-compatible. The result will contain all tuples from A for which there exist a matching tuple in B.

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