How does Newton's second law include the first law?

states that in the absence of a net force an object will not accelerate. The second law gives the definition of that net force in the famous equation:
##F = m * a##
where ##F## is the net force ##m## is the mass of the object and ##a## is the .
In the first law the net force is zero. Since mass is not zero for any object this makes the acceleration zero which matches the first law:
##0 = m * 0##
So the first law is really just a special case of the second law the case where ##F## and ##a## are zero.