It is also necessary to be repeated (renewed) before every obligatory prayer. He often attends mosques and surau throughout the country for the obligatory Friday prayers. The animal frieze was recognized as generally obligatory and customarily used. As was common in the late Soviet Union, "voluntary" actually meant "partially obligatory". The ears are said to indicate rites (voluntary and obligatory). One distinguishes between obligatory and optional arguments. Patronyms are part of full name and obligatory in formal messages. Transformational rules are of two kinds&colon; obligatory or optional. This creates some level of difficulty in performing the obligatory acts. No longer used on new elevators, where the sound is normally obligatory. Not obligatory and sometimes applied at universities in the Netherlands are the propaedeutic exams. The following two subsections consider both obligatory and optional pied-piping. Students who receive an "improbatur" in any of the obligatory exams fail the entire exam. Primary and secondary education is obligatory for everyone. Hematophagy is classified as either "obligatory" or "facultative".