A democratic republic is a form of government operating on principles adopted from a republic and a democracy. As a cross between two exceedingly similar systems, democratic republics may function on principles shared by both republics and democracies. While not all democracies are republics (constitutional monarchies) and not all republics are democracies, common definitions of the terms democracy and republic often feature overlapping concerns, suggesting that many democracies function as republics, and many republics operate on democratic principles, as shown by these definitions from the Oxford English Dictionary: Republic: "A state in which supreme power is held by the people and their elected representatives, and which has an elected or nominated president rather than a monarch." Democracy: "A system of government by the whole population or all the eligible members of a state, typically through elected representatives." Eugene Volokh of the UCLA School of Law notes that the United States exemplifies the varied nature of a constitutional republic—a country where some decisions (often local) are made by direct democratic processes, while others (often federal) are made by democratically elected representatives. As with many large systems, US governance is incompletely described by any single term. It also employs the concept, for instance, of a constitutional republic in which a court system is involved in matters of jurisprudence. However, these republics were, indeed, democratic republics that used Soviet democracy, a complicated form of indirect democracy.[citation needed] As with other democracies, not all persons in a democratic republic are necessarily citizens, and not all citizens are necessarily entitled to vote. Suffrage is commonly restricted by criteria such as voting age and sometimes by felony or imprisonment status.