human
What is a good Python function to count number of overlaps in two nested lists.
assistant
Here is a Python function to count number of overlaps in two nested lists

def count_overlaps(a, b):
    """Counts number of overlaps in two nested lists."""
    if len(a) == 0 or len(b) == 0:
        return 0
    return len(a) + len(b) - len(a + b)

# Enter the lists
a = [1,2,3]
b = [4,5,6]

# Calling the function
print((count_overlaps(a, b)))

#Example Output
# 0

#Remember to inspect code for bugs.