species_1 + species_3 -> species_2 + species_3
species_2 + species_3 -> species_2 + species_4
species_1 + species_4 -> species_2 + species_4
species_3 -> 0
species_1 -> 0
species_2 -> 0
species_4 -> 0
species_2 + species_5 -> species_6
species_6 -> species_2 + species_5
species_6 -> species_2
species_5 -> 0
species_6 -> 0
0 -> species_3
0 -> species_1
0 -> species_5