Check whether each input is paired with exactly one output
Verify that no input has more than one output
Confirm that every input in the domain is assigned an output
Use the vertical line test for graphs
Determine whether the relation passes the definition of a function
Ensure the rule consistently maps inputs to outputs
Check that repeated inputs always give the same output
Identify whether the relation is one-to-one or many-to-one, not one-to-many
Test ordered pairs for duplicate x-values with different y-values
Confirm the mapping diagram has one arrow from each input to one output