public static Set<Attribute> getReferences(Iterable<? extends Expression> exprs) {
        HashSet<Attribute> refs = new HashSet<>();
        for (Expression e : exprs) {
            refs.addAll(e.references());
        }
        return refs;
    }
Returns true when two expressions will always compute the same result, even if they differ
cosmetically (i.e. capitalization of names in attributes may be different).
indexr-query-opt/src/main/java/io/indexr/query/expr/Expression.java