Tiny renaming.
Code style.
Oops, single test was in broken state.

Fortunately, it passes after uncommenting.
Filter test has been extended to check false conditions.
Filtering: using logic operator mixins to reduce code duplication.
Filtering: `OR` operator can now be used in equal expressions.
Decomposition.
Less predicate now returns its true type.
Filtering: `LessEq` predicate has been implemented with && and || operators support.
Filtering: implementation of `Gt` predicate with && and || operators support.
Filtering: `GtEq` predicate has been implemented with && and || operators support.