theta a Xj n theta theta a Xj n theta b Yi Yj n c Xi theta b Yi Yj n theta c Xi n b Yi Yj n compartment_1 function_1 theta a species_3 n compartment_1 k1 species_1 compartment_1 function_2 theta b species_2 species_4 n c species_1 compartment_1 k1 species_2 compartment_1 function_1 theta a species_1 n compartment_1 k1 species_3 compartment_1 function_2 theta b species_2 species_4 n c species_3 compartment_1 k1 species_4