diff --git a/src/Algorithms/A20/A20.jl b/src/Algorithms/A20/A20.jl
index a01c49e57c..0127c67585 100644
--- a/src/Algorithms/A20/A20.jl
+++ b/src/Algorithms/A20/A20.jl
@@ -8,21 +8,24 @@ inputs in the Krylov subspace from [Althoff20](@citet).
 
 ### Fields
 
-- `δ`          -- step-size of the discretization
-- `max_order`  -- (optional, default: `5`) maximum zonotope order
+- `δ`            -- step-size of the discretization
+- `approx_model` -- (optional, default: `FirstOrderZonotope()`) approximation model
+- `max_order`    -- (optional, default: `5`) maximum zonotope order
 
 ### References
 
 See [Althoff20](@citet) and references therein.
 """
-struct A20{N} <: AbstractContinuousPost
+struct A20{N,AM} <: AbstractContinuousPost
     δ::N
+    approx_model::AM
     max_order::Int
 end
 
 # convenience constructor using keywords
-function A20(; δ::N, max_order::Int=5) where {N}
-    return A20(δ, max_order)
+# TODO change `FirstOrderZonotope` default
+function A20(; δ::N, approx_model::AM=FirstOrderZonotope(), max_order::Int=5) where {N,AM}
+    return A20(δ, approx_model, max_order)
 end
 
 step_size(alg::A20) = alg.δ
diff --git a/src/Algorithms/A20/post.jl b/src/Algorithms/A20/post.jl
index 73823339fc..660dbfc414 100644
--- a/src/Algorithms/A20/post.jl
+++ b/src/Algorithms/A20/post.jl
@@ -3,7 +3,14 @@
 # discrete post
 function post(alg::A20{N}, ivp::IVP{<:AbstractDiscreteSystem}, NSTEPS=nothing;
               Δt0::TimeInterval=zeroI, kwargs...) where {N}
-    @unpack δ, max_order = alg
+    @unpack δ, approx_model, max_order = alg
+    # TODO define these options in the algorithm struct
+    static = Val(get(kwargs, :static, false))
+    reduction_method = LazySets.GIR05()
+    dim = missing
+    ngens = missing
+    preallocate = Val(get(kwargs, :preallocate, true))
+    disjointness_method = NoEnclosure()
 
     if isnothing(NSTEPS)
         if haskey(kwargs, :NSTEPS)
@@ -25,7 +32,6 @@ function post(alg::A20{N}, ivp::IVP{<:AbstractDiscreteSystem}, NSTEPS=nothing;
     Ω0 = reduce_order(Ω0, max_order, reduction_method)
 
     # reconvert the set of initial states and state matrix, if needed
-    static = get(kwargs, :static, false)
     Ω0 = _reconvert(Ω0, static, dim, ngens)
     Φ = _reconvert(Φ, static, dim)
 
@@ -34,6 +40,7 @@ function post(alg::A20{N}, ivp::IVP{<:AbstractDiscreteSystem}, NSTEPS=nothing;
     ZT = typeof(Ω0)
     F = Vector{ReachSet{N,ZT}}(undef, NSTEPS)
 
+    # TODO currently uses GLGM06 algorithm
     if got_homogeneous
 
         #=
@@ -46,8 +53,7 @@ function post(alg::A20{N}, ivp::IVP{<:AbstractDiscreteSystem}, NSTEPS=nothing;
         end
         =#
 
-        reach_homog_GLGM06!(F, Ω0, Φ, NSTEPS, δ, max_order, X, preallocate, Δt0,
-                            disjointness_method)
+        reach_homog_GLGM06!(F, Ω0, Φ, NSTEPS, δ, X, preallocate, Δt0, disjointness_method)
     else
         # TODO: implement preallocate option for this scenario
         U = inputset(ivp)
diff --git a/src/ReachSets/TaylorModelReachSet.jl b/src/ReachSets/TaylorModelReachSet.jl
index 9f28ed2df7..68a52e5132 100644
--- a/src/ReachSets/TaylorModelReachSet.jl
+++ b/src/ReachSets/TaylorModelReachSet.jl
@@ -2,7 +2,7 @@
 # Taylor model reach set
 # ================================================================
 
-import ..Overapproximate: _overapproximate, _overapproximate_hparallelotope
+import .Overapproximate: _overapproximate, _overapproximate_hparallelotope
 
 """
     TaylorModelReachSet{N, S} <: AbstractTaylorModelReachSet{N}