Function parse_cardinality_expr 

fn parse_cardinality_expr<T>(
    pair: Pair<'_, Rule>,
) -> Result<IntegerExpression<T>, Error>
where
    T: Atomic + 'static,

Parses a constraint of the form Cardinality({p \in Processes : ProcessesLocations[p] = "loc0"}) into an IntegerExpression::Atom(Location::new("loc0"))

This function panics if you attempt to parse it into a type other then IntegerExpression<Location