Niddah, Chapter 6, Mishnah 8. The closing section of this chapter is built out of a long series of general rules, each one introduced by the word "kol," every case that has such and such also has such and such. In each of these rules two halachos are paired, and the Mishnah tells us in which direction the pairing runs: whatever is included in the first is automatically included in the second, but the reverse is not necessarily true. Our Mishnah presents one such pair, and it deals with two of the gifts that the Torah assigns to the kohen from a person's animals.
The first of the two is reishis hagez, the first of the shearing. When a person shears his flock, the first wool that comes off the animal is not simply his to use as he pleases; it is set aside and handed over to a kohen as a gift.
The second is matanos, the portions of an animal that is brought and slaughtered, certain designated parts of which belong to the kohen and are given to him as his gift.
The Mishnah's rule is: "Kol shechayav bereishis hagez chayav bematanos," every animal that carries the obligation of first shearing also carries the obligation of the priestly portions. Any animal from whose fleece reishis hagez must be given is likewise an animal from which the kohen receives his portions. There is no animal that falls into the category of first shearing while escaping the category of matanos; whatever is in the first group is automatically in the second.
The Mishnah then closes off the other direction: "Veyesh shechayav bematanos ve'eino chayav bereishis hagez," and there is that which is obligated in the priestly portions and is not obligated in the first of the shearing. The two categories are not identical in size. There are animals whose slaughter obligates the owner to give the designated portions to a kohen, yet no obligation of first shearing ever arises from them. So the overlap runs one way only: reishis hagez always brings matanos along with it, while matanos can stand entirely on its own.
This is the pattern to carry away from the Mishnah: the first halachah is contained within the second, the second reaches further than the first, and the Mishnah has taught us both halves of that relationship in a single line.