Is patent US 5,504,055 A, application Nr. 08/213,263 expired? It was filed on 15 Mar 1994 and issued on 2 April 1996.
For applications file prior to June 8th, 1995, the patent term is either 17 years from the issue date or 20 years from the filing date of the earliest U.S. or international (PCT) application to which priority is claimed (excluding provisional applications), the longer term applying. So this is either April 2, 2013 (17 years) or May 15, 2014 (20 years). Since May 15, 2014 is later, it is the expiration date for this patent unless there is an extension.