Critical Description
For non-deterministic expressions, they should be considered as not contained in the [[ExpressionSet]].
This is consistent with how we define `semanticEquals` between two expressions.
Otherwise, combining expressions will remove non-deterministic expressions which should be reserved.
E.g
Combine filters of
```
testRelation.where(Rand(0) > 0.1).where(Rand(0) > 0.1)
```
should result in
```
testRelation.where(Rand(0) > 0.1 && Rand(0) > 0.1)
```
