**Problem : **
For a given value of *x* and a
function *f*, how many values of
*f* (*x*) exist?

**Problem : **
Is the graph below a graph of a function?

**Problem : **
Is the graph below a graph of a function?

**Problem : **
Is the graph below a graph of a function?

**Problem : **
Is the graph below a graph of a function?

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