begin parameters
  A_fre     50
  A_flu     50
  B_tot     100
  D_tot     100
  E_tot     100
  k1f 1
  k1r 1
end parameters

begin molecule types
A(label~none~F,in_complex~none~C~E)
B
D
end molecule types

begin species
A(label~none,in_complex~none)  A_fre
A(label~F,in_complex~none)     A_flu
B()            B_tot
D()            D_tot
end species

begin reaction rules
A(in_complex~none) + B <-> A(in_complex~C) k1f, k1r
A(in_complex~C)    + D <-> A(in_complex~E) k1f, k1r
A(label~F) -> A(label~none)  k1f
end reaction rules

generate_network({overwrite=>1});
writeSBML({});