Oliver Kutz Frank Wolter Holger Sturm Nobu-Yuki Suzuki Michael Zakharyaschev Logics of metric spaces. 260-294 2003 4 ACM Trans. Comput. Log. 2 http://doi.acm.org/10.1145/635499.635504 db/journals/tocl/tocl4.html#KutzWSSZ03