No, if an open circle (representing a point) is on top of a closed circle (representing a filled-in point), it is not a function. In a function, each input (x-value) can have only one output (y-value). However, a closed circle represents a specific point on the graph, indicating that it is included in the function, while an open circle represents a point that is not included. When an open circle is above a closed circle, it violates the rule of a function because that specific input (x-value) would have two different outputs (y-values).
