Note 1.

The second step in the reaction (2X + Y becomes 3X) is the autocatalytic step. This reaction step will for example [ "for example", because in fact we have to do with only a model -- imagined to be real ] take place in the presence of a catalyst activated by X. The presence of that catalyst (for example an enzyme) consequently belongs to the (external) conditions imposed on the reaction.

With respect to the dynamical law (here given as a set of coupled differential equations) we must not think of this law as being transcendental. The law is implicitly and immanently contained in the constituents of the system. This law, (when) imagined as specified, now is the specific (in contrast with generic, not so specified) dynamical law. The specification could read for instance :   A = calcium sulphate, B = silver nitrate, etc., or whatever appropriate chemical substances.
In Natural Science the generic law is the more important, because it permits one -- while varying the specifications -- to deduce, and thus understand and explain , the specific behavior, i.e. the behavior belonging to a certain individual case, FROM a more general state of affairs, and in this way (i.e. by knowing the generic law) possessing potential knowledge of many individual cases.
For our purposes on the other hand, the specific dynamical law is the more important, because we (on this website) -- setting up an updated Substance-Accident Metaphysics -- are trying to ontologically understand an individual case (involving an existing uniform being with a specific -- not generic -- Essence). The assessed ontological status will then be the same for all other individual cases falling under the generic law.

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