species_1 + species_2 -> species_3
species_3 -> species_1 + species_2
species_3 -> species_2 + species_4
species_2 + species_4 -> species_5
species_5 -> species_2 + species_4
species_5 -> species_2 + species_6
species_13 + species_6 -> species_21
species_21 -> species_13 + species_6
species_21 -> species_13 + species_4
species_13 + species_4 -> species_22
species_22 -> species_13 + species_4
species_22 -> species_1 + species_13
species_23 -> species_1 + species_13
species_1 + species_13 -> species_23
species_7 + species_8 -> species_9
species_9 -> species_7 + species_8
species_9 -> species_10 + species_8
species_10 + species_8 -> species_11
species_11 -> species_10 + species_8
species_11 -> species_2 + species_8
species_13 + species_2 -> species_12
species_12 -> species_13 + species_2
species_12 -> species_10 + species_13
species_10 + species_13 -> species_14
species_14 -> species_10 + species_13
species_14 -> species_13 + species_7
species_15 -> species_13 + species_7
species_13 + species_7 -> species_15
species_16 + species_18 -> species_17
species_17 -> species_16 + species_18
species_17 -> species_18 + species_8
species_20 + species_8 -> species_19
species_19 -> species_20 + species_8
species_19 -> species_16 + species_20
species_2 + species_20 -> species_24
species_24 -> species_2 + species_20
species_24 -> species_10 + species_20
species_10 + species_20 -> species_25
species_25 -> species_10 + species_20
species_25 -> species_20 + species_7
species_26 -> species_20 + species_7
species_20 + species_7 -> species_26
species_27 -> species_16 + species_20
species_16 + species_20 -> species_27