diff --git a/doc/pathing.md b/doc/pathing.md
index e7f032a22..e5361143f 100644
--- a/doc/pathing.md
+++ b/doc/pathing.md
@@ -66,7 +66,7 @@ Returns connected components of the undirected graph of `g`.
 ```
 has_self_loop(g::Union{LightGraphs.DiGraph,LightGraphs.Graph})
 ```
-Returns true if `g` is has any self loops.
+Returns true if `g` has any self loops.
 
 ### attracting_components
 ```
diff --git a/src/LightGraphs.jl b/src/LightGraphs.jl
index 4c2cd812d..b25855b53 100644
--- a/src/LightGraphs.jl
+++ b/src/LightGraphs.jl
@@ -34,7 +34,7 @@ in_edges, out_edges, has_vertex, has_edge, is_directed,
 nv, ne, add_edge!, rem_edge!, add_vertex!, add_vertices!,
 indegree, outdegree, degree, degree_histogram, density, Δ, δ,
 Δout, Δin, δout, δin, neighbors, in_neighbors, out_neighbors,
-common_neighbors, all_neighbors, has_self_loop,
+common_neighbors, all_neighbors, has_self_loop, ordered,
 
 # distance
 eccentricity, diameter, periphery, radius, center,
@@ -95,7 +95,10 @@ a_star,
 readgraph, readgraphml, readgml, writegraphml, writegexf,
 
 # randgraphs
-erdos_renyi, watts_strogatz, random_regular_graph, random_regular_digraph, random_configuration_model
+erdos_renyi, watts_strogatz, random_regular_graph, random_regular_digraph, random_configuration_model,
+
+# edgeit - TODO EdgeItState could probably not be exported
+edge_it, in_edge_it, out_edge_it, EdgeIt, EdgeItState
 
 """An optimized graphs package.
 
@@ -117,6 +120,7 @@ LightGraphs
 include("core.jl")
     include("digraph.jl")
     include("graph.jl")
+        include("edgeit.jl")
         include("traversals/graphvisit.jl")
             include("traversals/bfs.jl")
             include("traversals/dfs.jl")
diff --git a/src/core.jl b/src/core.jl
index 830e1336f..e9b28d57b 100644
--- a/src/core.jl
+++ b/src/core.jl
@@ -20,6 +20,8 @@ src(e::Edge) = e.first
 """Return destination of an edge."""
 dst(e::Edge) = e.second
 
+ordered(e::Edge) = src(e) <= dst(e)
+
 @deprecate rev(e::Edge) reverse(e)
 
 ==(e1::Edge, e2::Edge) = (e1.first == e2.first && e1.second == e2.second)
@@ -30,16 +32,18 @@ end
 
 """A type representing an undirected graph."""
 type Graph
+    ne # number of edges
     vertices::UnitRange{Int}
-    edges::Set{Edge}
+    # edges::Set{Edge}
     fadjlist::Vector{Vector{Int}} # [src]: (dst, dst, dst)
     badjlist::Vector{Vector{Int}} # [dst]: (src, src, src)
 end
 
 """A type representing a directed graph."""
 type DiGraph
+    ne # number of edges
     vertices::UnitRange{Int}
-    edges::Set{Edge}
+    # edges::Set{Edge}
     fadjlist::Vector{Vector{Int}} # [src]: (dst, dst, dst)
     badjlist::Vector{Vector{Int}} # [dst]: (src, src, src)
 end
@@ -50,8 +54,8 @@ typealias SimpleGraph @compat(Union{Graph, DiGraph})
 """Return the vertices of a graph."""
 vertices(g::SimpleGraph) = g.vertices
 
-"""Return the edges of a graph."""
-edges(g::SimpleGraph) = g.edges
+"""Return an iterator to the edges of a graph."""
+edges(g::SimpleGraph) = edge_it(g)
 
 """Returns the forward adjacency list of a graph.
 
@@ -118,7 +122,7 @@ has_vertex(g::SimpleGraph, v::Int) = v in vertices(g)
 """The number of vertices in `g`."""
 nv(g::SimpleGraph) = length(vertices(g))
 """The number of edges in `g`."""
-ne(g::SimpleGraph) = length(edges(g))
+ne(g::SimpleGraph) = g.ne
 
 """Add a new edge to `g` from `src` to `dst`.
 
@@ -194,8 +198,8 @@ neighbors(g::SimpleGraph, v::Int) = out_neighbors(g, v)
 common_neighbors(g::SimpleGraph, u::Int, v::Int) = intersect(neighbors(g,u), neighbors(g,v))
 
 function copy{T<:SimpleGraph}(g::T)
-    return T(g.vertices,copy(g.edges),deepcopy(g.fadjlist),deepcopy(g.badjlist))
+    return T(g.ne, g.vertices,deepcopy(g.fadjlist),deepcopy(g.badjlist))
 end
 
-"Returns true if `g` is has any self loops."
+"Returns true if `g` has any self loops."
 has_self_loop(g::SimpleGraph) = any(v->has_edge(g, v, v), vertices(g))
diff --git a/src/digraph.jl b/src/digraph.jl
index 99acf1a5b..964d2c6cc 100644
--- a/src/digraph.jl
+++ b/src/digraph.jl
@@ -13,7 +13,7 @@ function DiGraph(n::Int)
         push!(badjlist, @compat(Vector{Int}()))
         push!(fadjlist, @compat(Vector{Int}()))
     end
-    return DiGraph(1:n, Set{Edge}(), badjlist, fadjlist)
+    return DiGraph(0, 1:n, badjlist, fadjlist)
 end
 
 DiGraph() = DiGraph(0)
@@ -50,17 +50,14 @@ end
 
 function DiGraph(g::Graph)
     h = DiGraph(nv(g))
-    for e in edges(g)
-        push!(h.edges,e)
-        push!(h.edges,reverse(e))
-    end
     h.fadjlist = copy(fadj(g))
     h.badjlist = copy(badj(g))
     return h
 end
 
+#warning: could be slow,
 function ==(g::DiGraph, h::DiGraph)
-    return (vertices(g) == vertices(h)) && (edges(g) == edges(h))
+    return (vertices(g) == vertices(h)) && (Set(edges(g)) == Set(edges(h)))
 end
 
 is_directed(g::DiGraph) = true
@@ -68,7 +65,7 @@ is_directed(g::DiGraph) = true
 function unsafe_add_edge!(g::DiGraph, e::Edge)
     push!(g.fadjlist[src(e)], dst(e))
     push!(g.badjlist[dst(e)], src(e))
-    push!(g.edges, e)
+    g.ne+=1
     return e
 end
 
@@ -80,7 +77,8 @@ function rem_edge!(g::DiGraph, e::Edge)
     deleteat!(g.fadjlist[src(e)], i)
     i = findfirst(g.badjlist[dst(e)], src(e))
     deleteat!(g.badjlist[dst(e)], i)
-    return pop!(g.edges, e)
+    g.ne -= 1
+    return e
 end
 
 has_edge(g::DiGraph, e::Edge) = e in edges(g)
diff --git a/src/edgeit.jl b/src/edgeit.jl
new file mode 100644
index 000000000..49333ae26
--- /dev/null
+++ b/src/edgeit.jl
@@ -0,0 +1,66 @@
+import Base: start, next, done, length, show,
+            in, ==
+
+type EdgeItState
+    it::Int
+    v::Int
+    k::Int
+end
+
+type EdgeIt
+    m::Int
+    adj::Vector{Vector{Int}}
+    start::EdgeItState # =[it, v, k]
+    directed::Bool
+end
+
+edge_it(g::Graph) = EdgeIt(ne(g), g.fadjlist, EdgeItState(1,1,1), false)
+edge_it(g::DiGraph) = EdgeIt(ne(g), g.fadjlist, EdgeItState(1,1,1), true)
+
+start(eit::EdgeIt) = eit.start
+done(eit::EdgeIt, state::EdgeItState) = state.it > eit.m
+function next(eit::EdgeIt, state::EdgeItState)
+    # println("$eit, $state")
+    assert(state.v <= length(eit.adj))
+    u = 0
+    while state.k <= length(eit.adj[state.v])
+        u  = eit.adj[state.v][state.k]
+        eit.directed && break
+        u >= state.v && break
+        state.k += 1
+    end
+    while state.k > length(eit.adj[state.v])
+        state.k = 1
+        state.v += 1
+        while state.k <= length(eit.adj[state.v])
+            u  = eit.adj[state.v][state.k]
+            eit.directed && break
+            u >= state.v && break
+            state.k += 1
+        end
+    end
+    e = !eit.directed && u < state.v ? Edge(u, state.v) : Edge(state.v, u)
+    state.k += 1
+    state.it += 1
+    return (e, state)
+end
+length(eit::EdgeIt) = eit.m
+
+function in(e::Edge, eit::EdgeIt)
+    s = src(e)
+    t = dst(e)
+    n = length(eit.adj)
+    !(1 <=  s <= n) && return false
+    !(1 <=  t <= n) && return false
+    return t in eit.adj[s]
+end
+
+#TODO implement using a loop and ∈, so that no memory is allocated
+==(e1::EdgeIt, e2::Set{Edge}) = Set{Edge}(e1) == e2
+==(e1::Set{Edge}, e2::EdgeIt) = e1 == Set{Edge}(e2)
+==(e1::EdgeIt, e2::EdgeIt) = Set{Edge}(e1) == Set{Edge}(e2)
+
+
+
+show(io::IO, eit::EdgeIt) = write(io, "edgeit $(eit.m)")
+show(io::IO, s::EdgeItState) = write(io, "edgeitstate [ $(s.it),$(s.v),$(s.k) ]")
diff --git a/src/graph.jl b/src/graph.jl
index 70062e3c3..413d420e5 100644
--- a/src/graph.jl
+++ b/src/graph.jl
@@ -17,7 +17,7 @@ function Graph(n::Int)
         push!(badjlist, @compat(Vector{Int}()))
         push!(fadjlist, @compat(Vector{Int}()))
     end
-    return Graph(1:n, Set{Edge}(), badjlist, fadjlist)
+    return Graph(0, 1:n, badjlist, fadjlist)
 end
 
 Graph() = Graph(0)
@@ -48,6 +48,7 @@ function Graph(g::DiGraph)
     return h
 end
 
+#warning: could be slow
 function ==(g::Graph, h::Graph)
     gdigraph = DiGraph(g)
     hdigraph = DiGraph(h)
@@ -65,16 +66,12 @@ function unsafe_add_edge!(g::Graph, e::Edge)
         push!(g.fadjlist[dst(e)], src(e))
         push!(g.badjlist[src(e)], dst(e))
     end
-    push!(g.edges, e)
+    g.ne += 1
     return e
 end
 
 function rem_edge!(g::Graph, e::Edge)
-    if !(e in edges(g))
-        reve = reverse(e)
-        (reve in edges(g)) || error("Edge $e is not in graph")
-        e = reve
-    end
+    (e in edges(g)) || error("Edge $e is not in graph")
 
     i = findfirst(g.fadjlist[src(e)], dst(e))
     deleteat!(g.fadjlist[src(e)], i)
@@ -84,7 +81,8 @@ function rem_edge!(g::Graph, e::Edge)
     deleteat!(g.fadjlist[dst(e)], i)
     i = findfirst(g.badjlist[src(e)], dst(e))
     deleteat!(g.badjlist[src(e)], i)
-    return pop!(g.edges, e)
+    g.ne -= 1
+    return ordered(e) ? e : reverse(e)
 end
 
 
diff --git a/src/operators.jl b/src/operators.jl
index 2c6729237..2aff26881 100644
--- a/src/operators.jl
+++ b/src/operators.jl
@@ -44,10 +44,6 @@ end
 function reverse!(g::DiGraph)
     gne = ne(g)
     reve = Set{Edge}()
-    for e in edges(g)
-        push!(reve, reverse(e))
-    end
-    g.edges = reve
     g.fadjlist, g.badjlist = g.badjlist, g.fadjlist
     return g
 end
diff --git a/test/core.jl b/test/core.jl
index cc86d474a..6974a1137 100644
--- a/test/core.jl
+++ b/test/core.jl
@@ -22,7 +22,14 @@ add_edge!(h, 3, 5)
 
 @test sprint(show, e1) == "edge 1 - 2"
 @test vertices(g) == 1:5
+i = 0
+for e in edges(g)
+    i+=1
+end
+@test i == 5
+@test has_edge(g,3,5)
 @test edges(g) == Set([e1, e2, e3, e4, e5])
+@test Set{Edge}(edges(g)) == Set([e1, e2, e3, e4, e5])
 
 @test degree(g) == [3, 2, 2, 1, 2]
 @test indegree(g) == [3, 2, 2, 1, 2]
@@ -65,13 +72,33 @@ add_edge!(h, 3, 5)
 @test common_neighbors(g, 2, 3) == [1, 5]
 @test common_neighbors(h, 2, 3) == [5]
 
+@test ne(g) == 5
 @test rem_edge!(g, 1, 2) == e1
+@test ne(g) == 4
+eit = edges(g)
+@test eit.m == 4
+state = start(eit)
+@test state.it == 1
+@test state.v == 1
+@test state.k == 1
+# @test edges(g) == EdgeIt(4, g.fadjlist, EdgeItState(1,1,1),  false)
+
 @test_throws ErrorException rem_edge!(g, 2, 1)
 add_edge!(g, 1, 2)
+@test ne(g) == 5
+eit = edges(g)
+@test eit.m == 5
+state = start(eit)
+@test state.it == 1
+@test state.v == 1
+@test state.k == 1
+
+@test Edge(2, 1) in edges(g)
+@test Edge(1, 2) in edges(g)
 @test rem_edge!(g, 2, 1) == e1
 
 @test rem_edge!(h, 1, 2) == e1
 @test_throws ErrorException rem_edge!(h, 1, 2)
 
 @test g == copy(g)
-@test !(g === copy(g))
\ No newline at end of file
+@test !(g === copy(g))
diff --git a/test/runtests.jl b/test/runtests.jl
index ed9ea3e5b..315b4185f 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -43,10 +43,9 @@ a1 = Graph(adjmx1)
 a2 = DiGraph(adjmx2)
 
 tests = [
+    "core",
     "randgraphs",
     "graphdigraph",
-    "persistence",
-    "core",
     "smallgraphs",
     "shortestpaths/astar",
     "shortestpaths/bellman-ford",
@@ -65,7 +64,8 @@ tests = [
     "centrality/degree",
     "centrality/katz",
     "centrality/pagerank",
-    "subgraphs"
+    "subgraphs",
+    "persistence"
     ]