The practicum is intended to prepare students for the internship/residency. There is no centralized selection process for internship or residency positions. Subspecialties require the completion of a fellowship after residency. Admission rates vary according to the residency of applicants. In Canada, an ophthalmology residency after medical school is undertaken. Applying for residency positions in radiology is relatively competitive. These safeguards include proving one's residency and eligibility. In Greece, licensed physicians are eligible to apply for a position in a residency program. In Colombia, fully licensed physicians are eligible to compete for seats in residency programs. These may be permits for temporary residency, or permanent residency. Congress reacted by carving out a specific exception in antitrust law for medical residency. Some established themselves to continue practice beyond the residency stage. The US is well known for its excellence in emergency medicine residency training programs. It also led to the establishment of a permanent British Residency. However, they do not count as marriages for the purpose of granting spousal residency rights.