The model contains three varying parameters called S1, S2 and S3 and two constant parameters called k1 and k2. (Note that indeed S1, S2 and S3 are parameters and not species in this model.)

The model contains three rules defined as:

Type Variable Formula
Rate S1 k2 · S3 − k1 · S1 · S2
Rate S2 k2 · S3 − k1 · S1 · S2
Rate S3 k1 · S1 · S2 − k2 · S3

The model contains one event that assigns values to parameters S1 and S2:

Trigger Delay Assignments
Event1 S1 < 0.75 S2 = 1.5
S1 = S2

Note that the event assignments should happen simultaneously, not sequentially; i.e., the value of S2 assigned to S1 is the value at the point at which the event was triggered.

The initial conditions are as follows:

Value Units
Initial amount of S1 1.0 any
Initial amount of S2 2.0 same as S1
Initial amount of S3 1.0 same as S1
Value of parameter k1 0.75 (unit of S1)-1 second-1
Value of parameter k2 0.25 second-1