diff --git a/src/face_crawler.rs b/src/face_crawler.rs
index fb7e1d7..9e80789 100644
--- a/src/face_crawler.rs
+++ b/src/face_crawler.rs
@@ -1,3 +1,6 @@
+use crate::physics::Body;
+use crate::integer::Time;
+
 struct VertexId(usize);
 struct EdgeId(usize);
 struct FaceId(usize);
@@ -19,3 +22,58 @@ enum Transition{
 	NextState(State),
 	Hit(FaceId,Time),
 }
+
+impl State{
+	fn next_transition(&self,mesh:&VirtualMesh,time_limit:Time)->Transition{
+		//conflicting derivative means it crosses in the wrong direction.
+		match self.fev{
+			FEV::Face(face_id)=>{
+				//test own face collision time
+				//test each edge collision time, ignoring edges with zero or conflicting derivative
+				//if face: return (Face,Time)
+				//if edge: goto edge
+			},
+			FEV::Edge(edge_id)=>{
+				//test each face collision time, ignoring faces with zero or conflicting derivative
+				//test each vertex collision time, ignoring vertices with zero or conflicting derivative
+				//if face: goto face
+				//if vertex: goto vertex
+			},
+			FEV::Vertex(vertex_id)=>{
+				//test each edge collision time, ignoring edges with zero or conflicting derivative
+				//goto edge
+			},
+		}
+	}
+}
+
+//Note that a face on a minkowski mesh refers to a pair of fevs on the meshes it's summed from
+//(face,vertex)
+//(edge,edge)
+//(vertex,face)
+
+struct VirtualMesh{
+	//???
+}
+
+impl VirtualMesh{
+	pub fn minkowski_sum(mesh0:&PhysicsMesh,mesh1:&PhysicsMesh)->Self{
+		//?????
+	}
+	pub fn predict_collision(&self,body:&Body,time:Time,time_limit:Time)->Option<(FaceId,Time)>{
+		//mesh.closest_point returns if the point is on a face, edge or vertex
+		let (point,fev)=self.closest_point(body.extrapolated_position(time));
+		let mut state=State{
+			time,
+			fev,
+		};
+		//it would be possible to write down the point of closest approach...
+		loop{
+			match state.next_transition(self,time_limit){
+				Transition::Miss=>return None,
+				Transition::NextState(next_state)=>state=next_state,
+				Transition::Hit(hit_face,hit_time)=>return Some((hit_face,hit_time)),
+			}
+		}
+	}
+}