function main(β, γ, μ, n)
    @grounding begin
        S => Noun(person)
        I => Noun(patient)
        R => Noun(person)
        λ₁ => Verb(h3n2)
        λ₂ => Verb(treatment)
        λ₃ => Verb(loss_of_immunity)
    end

    @variables S, I, R, β, γ, μ, n

    Δ = [
        (S~S-1, I~I+1),
        (I~I-1, R~R+1),
        (R~R-1, S~S+1)
    ]

    ϕ = [
        S > 0 && I > 0,
        I > 0,
        R > 0,
    ]

    Λ = [
        β*S*I/n,
        γ*I,
        μ*R
    ]

    # generate discrete petri model
    m = Petri.Model([S, I, R], Δ, ϕ, Λ)

    # create instance of petri model with initial conditions
    p = Petri.Problem(m, (100, 1, 0, 0.5, 0.15, 0.05, 101), 150)

    # discrete solution
    soln = Petri.solve(p)
end