presto-main/src/main/java/io/prestosql/sql/planner/iterative/rule/PushProjectionThroughExchange.java/PushProjectionThroughExchange/isSymbolToSymbolProjection
class PushProjectionThroughExchange:    private static boolean isSymbolToSymbolProjection(ProjectNode project)
    {
        return project.getAssignments().getExpressions().stream().allMatch(e -> e instanceof SymbolReference);
    }