2 ⋅ x {\displaystyle 2\cdot x} is an output expression producing members of the new set from members of the input set that satisfy the predicate expression. { } {\displaystyle \{\}} braces indicate that the result is a set ∣ {\displaystyle \mid } , {\displaystyle ,} the vertical bar is read as "SUCH THAT". The bar and the colon ":" are used interchangeably. commas separate the predicates and can be read as "AND" .