diff --git a/Project.toml b/Project.toml
index 3f5cd526..432678e2 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "ITensorNetworks"
 uuid = "2919e153-833c-4bdc-8836-1ea460a35fc7"
 authors = ["Matthew Fishman <mfishman@flatironinstitute.org> and contributors"]
-version = "0.3.10"
+version = "0.4.0"
 
 [deps]
 AbstractTrees = "1520ce14-60c1-5f80-bbc7-55ef81b5835c"
@@ -37,13 +37,13 @@ Combinatorics = "1"
 Compat = "3, 4"
 DataGraphs = "0.1.7"
 DataStructures = "0.18"
-Dictionaries = "0.3.15"
+Dictionaries = "0.4"
 Distributions = "0.25.86"
 DocStringExtensions = "0.8, 0.9"
 Graphs = "1.8"
 GraphsFlows = "0.1.1"
 ITensors = "0.3.23"
-IsApprox = "0.1.7"
+IsApprox = "0.1"
 IterTools = "1.4.0"
 KrylovKit = "0.6.0"
 NamedGraphs = "0.1.11"
diff --git a/src/solvers/contract.jl b/src/solvers/contract.jl
index 588d35ae..ed55a729 100644
--- a/src/solvers/contract.jl
+++ b/src/solvers/contract.jl
@@ -12,7 +12,7 @@ function contract_updater(
   v = ITensor(true)
   projected_operator = projected_operator![]
   for j in sites(projected_operator)
-    v *= projected_operator.psi0[j]
+    v *= init_state(projected_operator)[j]
   end
   vp = contract(projected_operator, v)
   return vp, (;)
diff --git a/src/treetensornetworks/projttns/abstractprojttn.jl b/src/treetensornetworks/projttns/abstractprojttn.jl
index 9f6da826..e3b0e140 100644
--- a/src/treetensornetworks/projttns/abstractprojttn.jl
+++ b/src/treetensornetworks/projttns/abstractprojttn.jl
@@ -1,5 +1,11 @@
 abstract type AbstractProjTTN{V} end
 
+environments(::AbstractProjTTN) = error("Not implemented")
+operator(::AbstractProjTTN) = error("Not implemented")
+pos(::AbstractProjTTN) = error("Not implemented")
+
+underlying_graph(P::AbstractProjTTN) = error("Not implemented")
+
 copy(::AbstractProjTTN) = error("Not implemented")
 
 set_nsite(::AbstractProjTTN, nsite) = error("Not implemented")
@@ -7,11 +13,10 @@ set_nsite(::AbstractProjTTN, nsite) = error("Not implemented")
 # silly constructor wrapper
 shift_position(::AbstractProjTTN, pos) = error("Not implemented")
 
-make_environment!(::AbstractProjTTN, psi, e) = error("Not implemented")
-
-underlying_graph(P::AbstractProjTTN) = underlying_graph(P.H)
-
-pos(P::AbstractProjTTN) = P.pos
+set_environments(p::AbstractProjTTN, environments) = error("Not implemented")
+set_environment(p::AbstractProjTTN, edge, environment) = error("Not implemented")
+make_environment!(P::AbstractProjTTN, psi, e) = error("Not implemented")
+make_environment(P::AbstractProjTTN, psi, e) = error("Not implemented")
 
 Graphs.edgetype(P::AbstractProjTTN) = edgetype(underlying_graph(P))
 
@@ -43,8 +48,8 @@ function internal_edges(P::AbstractProjTTN{V})::Vector{NamedEdge{V}} where {V}
 end
 
 environment(P::AbstractProjTTN, edge::Pair) = environment(P, edgetype(P)(edge))
-function environment(P::AbstractProjTTN{V}, edge::NamedEdge{V})::ITensor where {V}
-  return P.environments[edge]
+function environment(P::AbstractProjTTN, edge::AbstractEdge)
+  return environments(P)[edge]
 end
 
 # there has to be a better way to do this...
@@ -69,9 +74,9 @@ function contract(P::AbstractProjTTN, v::ITensor)::ITensor
   else
     itensor_map = Union{ITensor,OneITensor}[] # TODO: will a Hamiltonian TTN tensor ever be a OneITensor?
     for s in sites(P)
-      site_envs = filter(hascommoninds(P.H[s]), environments)
+      site_envs = filter(hascommoninds(operator(P)[s]), environments)
       frst, scnd, rst = _separate_first_two(site_envs)
-      site_tensors = vcat(frst, scnd, P.H[s], rst)
+      site_tensors = vcat(frst, scnd, operator(P)[s], rst)
       append!(itensor_map, site_tensors)
     end
   end
@@ -103,9 +108,9 @@ end
 (P::AbstractProjTTN)(v::ITensor) = product(P, v)
 
 function Base.eltype(P::AbstractProjTTN)::Type
-  ElType = eltype(P.H(first(sites(P))))
+  ElType = eltype(operator(P)(first(sites(P))))
   for v in sites(P)
-    ElType = promote_type(ElType, eltype(P.H[v]))
+    ElType = promote_type(ElType, eltype(operator(P)[v]))
   end
   for e in incident_edges(P)
     ElType = promote_type(ElType, eltype(environments(P, e)))
@@ -121,25 +126,36 @@ function Base.size(P::AbstractProjTTN)::Tuple{Int,Int}
     end
   end
   for j in sites(P)
-    for i in inds(P.H[j])
+    for i in inds(operator(P)[j])
       plev(i) > 0 && (d *= dim(i))
     end
   end
   return (d, d)
 end
 
-function position(
-  P::AbstractProjTTN{V}, psi::TTN{V}, pos::Union{Vector{<:V},NamedEdge{V}}
-) where {V}
-  # shift position
+function position(P::AbstractProjTTN, psi::AbstractTTN, pos)
   P = shift_position(P, pos)
-  # invalidate environments corresponding to internal edges
-  for e in internal_edges(P)
-    unset!(P.environments, e)
-  end
-  # make all environments surrounding new position
+  P = invalidate_environments(P)
+  P = make_environments(P, psi)
+  return P
+end
+
+function invalidate_environments(P::AbstractProjTTN)
+  ie = internal_edges(P)
+  newenvskeys = filter(!in(ie), keys(environments(P)))
+  P = set_environments(P, getindices(environments(P), newenvskeys))
+  return P
+end
+
+function invalidate_environment(P::AbstractProjTTN, e::AbstractEdge)
+  newenvskeys = filter(!isequal(e), keys(environments(P)))
+  P = set_environments(P, getindices(environments(P), newenvskeys))
+  return P
+end
+
+function make_environments(P::AbstractProjTTN, psi::AbstractTTN)
   for e in incident_edges(P)
-    make_environment!(P, psi, e)
+    P = make_environment(P, psi, e)
   end
   return P
 end
diff --git a/src/treetensornetworks/projttns/projttn.jl b/src/treetensornetworks/projttns/projttn.jl
index 18baa3e2..725650b2 100644
--- a/src/treetensornetworks/projttns/projttn.jl
+++ b/src/treetensornetworks/projttns/projttn.jl
@@ -3,15 +3,21 @@ ProjTTN
 """
 struct ProjTTN{V} <: AbstractProjTTN{V}
   pos::Union{Vector{<:V},NamedEdge{V}} # TODO: cleanest way to specify effective Hamiltonian position?
-  H::TTN{V}
+  operator::TTN{V}
   environments::Dictionary{NamedEdge{V},ITensor}
 end
 
-function ProjTTN(H::TTN)
-  return ProjTTN(vertices(H), H, Dictionary{edgetype(H),ITensor}())
+function ProjTTN(operator::TTN)
+  return ProjTTN(vertices(operator), operator, Dictionary{edgetype(operator),ITensor}())
 end
 
-copy(P::ProjTTN) = ProjTTN(P.pos, copy(P.H), copy(P.environments))
+copy(P::ProjTTN) = ProjTTN(pos(P), copy(operator(P)), copy(environments(P)))
+
+#accessors for fields
+environments(p::ProjTTN) = p.environments
+operator(p::ProjTTN) = p.operator
+underlying_graph(P::ProjTTN) = underlying_graph(operator(P))
+pos(P::ProjTTN) = P.pos
 
 # trivial if we choose to specify position as above; only kept to allow using alongside
 # ProjMPO
@@ -20,38 +26,45 @@ function set_nsite(P::ProjTTN, nsite)
 end
 
 function shift_position(P::ProjTTN, pos)
-  return ProjTTN(pos, P.H, P.environments)
+  return ProjTTN(pos, operator(P), environments(P))
+end
+
+set_environments(p::ProjTTN, environments) = ProjTTN(pos(p), operator(p), environments)
+set_environment(p::ProjTTN, edge, env) = set_environment!(copy(p), edge, env)
+function set_environment!(p::ProjTTN, edge, env)
+  set!(environments(p), edge, env)
+  return p
 end
 
-function make_environment!(P::ProjTTN{V}, psi::TTN{V}, e::NamedEdge{V})::ITensor where {V}
+function make_environment(P::ProjTTN, state::AbstractTTN, e::AbstractEdge)
   # invalidate environment for opposite edge direction if necessary
-  reverse(e) ∈ incident_edges(P) || unset!(P.environments, reverse(e))
+  reverse(e) ∈ incident_edges(P) || (P = invalidate_environment(P, reverse(e)))
   # do nothing if valid environment already present
-  if haskey(P.environments, e)
-    env = environment(P, e)
-  else
+  if !haskey(environments(P), e)
     if is_leaf(underlying_graph(P), src(e))
       # leaves are easy
-      env = psi[src(e)] * P.H[src(e)] * dag(prime(psi[src(e)]))
+      env = state[src(e)] * operator(P)[src(e)] * dag(prime(state[src(e)]))
     else
       # construct by contracting neighbors
       neighbor_envs = ITensor[]
       for n in setdiff(neighbors(underlying_graph(P), src(e)), [dst(e)])
-        push!(neighbor_envs, make_environment!(P, psi, edgetype(P)(n, src(e))))
+        P = make_environment(P, state, edgetype(P)(n, src(e)))
+        push!(neighbor_envs, environment(P, edgetype(P)(n, src(e))))
       end
       # manually heuristic for contraction order: two environments, site tensors, then
       # other environments
       frst, scnd, rst = _separate_first_two(neighbor_envs)
-      itensor_map = vcat(psi[src(e)], frst, scnd, P.H[src(e)], dag(prime(psi[src(e)])), rst)
+      itensor_map = vcat(
+        state[src(e)], frst, scnd, operator(P)[src(e)], dag(prime(state[src(e)])), rst
+      )
       # TODO: actually use optimal contraction sequence here
       env = reduce(*, itensor_map)
     end
-    # cache
-    set!(P.environments, e, env)
+    P = set_environment(P, e, env)
   end
   @assert(
-    hascommoninds(environment(P, e), psi[src(e)]),
+    hascommoninds(environment(P, e), state[src(e)]),
     "Something went wrong, probably re-orthogonalized this edge in the same direction twice!"
   )
-  return env
+  return P
 end
diff --git a/src/treetensornetworks/projttns/projttn_apply.jl b/src/treetensornetworks/projttns/projttn_apply.jl
index 67b8980b..d4f691b7 100644
--- a/src/treetensornetworks/projttns/projttn_apply.jl
+++ b/src/treetensornetworks/projttns/projttn_apply.jl
@@ -1,16 +1,24 @@
 struct ProjTTNApply{V} <: AbstractProjTTN{V}
   pos::Union{Vector{<:V},NamedEdge{V}}
-  psi0::TTN{V}
-  H::TTN{V}
+  init_state::TTN{V}
+  operator::TTN{V}
   environments::Dictionary{NamedEdge{V},ITensor}
 end
 
-function ProjTTNApply(psi0::TTN, H::TTN)
-  return ProjTTNApply(vertextype(H)[], psi0, H, Dictionary{edgetype(H),ITensor}())
+environments(p::ProjTTNApply) = p.environments
+operator(p::ProjTTNApply) = p.operator
+underlying_graph(p::ProjTTNApply) = underlying_graph(operator(p))
+pos(p::ProjTTNApply) = p.pos
+init_state(p::ProjTTNApply) = p.init_state
+
+function ProjTTNApply(init_state::AbstractTTN, operator::AbstractTTN)
+  return ProjTTNApply(
+    vertextype(operator)[], init_state, operator, Dictionary{edgetype(operator),ITensor}()
+  )
 end
 
 function copy(P::ProjTTNApply)
-  return ProjTTNApply(P.pos, copy(P.psi0), copy(P.H), copy(P.environments))
+  return ProjTTNApply(P.pos, copy(init_state(P)), copy(operator(P)), copy(environments(P)))
 end
 
 function set_nsite(P::ProjTTNApply, nsite)
@@ -18,40 +26,48 @@ function set_nsite(P::ProjTTNApply, nsite)
 end
 
 function shift_position(P::ProjTTNApply, pos)
-  return ProjTTNApply(pos, P.psi0, P.H, P.environments)
+  return ProjTTNApply(pos, init_state(P), operator(P), environments(P))
+end
+
+function set_environments(p::ProjTTNApply, environments)
+  return ProjTTNApply(pos(p), init_state(p), operator(p), environments)
 end
 
-function make_environment!(
-  P::ProjTTNApply{V}, psi::TTN{V}, e::NamedEdge{V}
-)::ITensor where {V}
+set_environment(p::ProjTTNApply, edge, env) = set_environment!(copy(p), edge, env)
+function set_environment!(p::ProjTTNApply, edge, env)
+  set!(environments(p), edge, env)
+  return p
+end
+
+function make_environment(P::ProjTTNApply, state::AbstractTTN, e::AbstractEdge)
   # invalidate environment for opposite edge direction if necessary
-  reverse(e) ∈ incident_edges(P) || unset!(P.environments, reverse(e))
+  reverse(e) ∈ incident_edges(P) || (P = invalidate_environment(P, reverse(e)))
   # do nothing if valid environment already present
-  if haskey(P.environments, e)
-    env = environment(P, e)
-  else
+  if !haskey(environments(P), e)
     if is_leaf(underlying_graph(P), src(e))
       # leaves are easy
-      env = P.psi0[src(e)] * P.H[src(e)] * dag(psi[src(e)])
+      env = init_state(P)[src(e)] * operator(P)[src(e)] * dag(state[src(e)])
     else
       # construct by contracting neighbors
       neighbor_envs = ITensor[]
       for n in setdiff(neighbors(underlying_graph(P), src(e)), [dst(e)])
-        push!(neighbor_envs, make_environment!(P, psi, edgetype(P)(n, src(e))))
+        P = make_environment(P, state, edgetype(P)(n, src(e)))
+        push!(neighbor_envs, environment(P, edgetype(P)(n, src(e))))
       end
       # manually heuristic for contraction order: two environments, site tensors, then
       # other environments
       frst, scnd, rst = _separate_first_two(neighbor_envs)
-      itensor_map = vcat(P.psi0[src(e)], frst, scnd, P.H[src(e)], dag(psi[src(e)]), rst)
+      itensor_map = vcat(
+        init_state(P)[src(e)], frst, scnd, operator(P)[src(e)], dag(state[src(e)]), rst
+      ) # no prime here in comparison to the same routine for Projttn
       # TODO: actually use optimal contraction sequence here
       env = reduce(*, itensor_map)
     end
-    # cache
-    set!(P.environments, e, env)
+    P = set_environment(P, e, env)
   end
   @assert(
-    hascommoninds(environment(P, e), psi[src(e)]),
+    hascommoninds(environment(P, e), state[src(e)]),
     "Something went wrong, probably re-orthogonalized this edge in the same direction twice!"
   )
-  return env
+  return P
 end
diff --git a/test/test_treetensornetworks/test_position.jl b/test/test_treetensornetworks/test_position.jl
new file mode 100644
index 00000000..9e8f96bb
--- /dev/null
+++ b/test/test_treetensornetworks/test_position.jl
@@ -0,0 +1,47 @@
+using ITensors
+using ITensorNetworks
+using ITensorNetworks: position, environments
+using Test
+
+@testset "ProjTTN position" begin
+  # make a nontrivial TTN state and TTN operator
+
+  auto_fermion_enabled = ITensors.using_auto_fermion()
+  use_qns = true
+  cutoff = 1e-12
+
+  tooth_lengths = fill(2, 3)
+  c = named_comb_tree(tooth_lengths)
+  if use_qns  # test whether autofermion breaks things when using non-fermionic QNs
+    ITensors.enable_auto_fermion()
+  else        # when using no QNs, autofermion breaks # ToDo reference Issue in ITensors
+    ITensors.disable_auto_fermion()
+  end
+  s = siteinds("S=1/2", c; conserve_qns=use_qns)
+
+  os = ITensorNetworks.heisenberg(c)
+
+  H = TTN(os, s)
+
+  d = Dict()
+  for (i, v) in enumerate(vertices(s))
+    d[v] = isodd(i) ? "Up" : "Dn"
+  end
+  states = v -> d[v]
+  psi = TTN(s, states)
+
+  # actual test, verifies that position is out of place
+  vs = vertices(s)
+  PH = ProjTTN(H)
+  PH = position(PH, psi, [vs[2]])
+  original_keys = deepcopy(keys(environments(PH)))
+  # test out-of-placeness of position
+  PHc = position(PH, psi, [vs[2], vs[5]])
+  @test keys(environments(PH)) == original_keys
+  @test keys(environments(PHc)) != original_keys
+
+  if !auto_fermion_enabled
+    ITensors.disable_auto_fermion()
+  end
+end
+nothing