use extern crate num only once

src/sim_elements.rs

@@ -1,7 +1,5 @@
-extern crate num;
-
 use vector::Vector2;
-use num::{Float,Integer,NumCast};
+use num::{self,Float,Integer,NumCast};
 use simulation::SimData;
 
 pub trait Simulable<T,U> where T: Float, U: Integer {
@@ -40,4 +38,4 @@ impl<T,U> Simulable<T,U> for Planet<T> where T: Float, U: Integer + NumCast {
         my_data.vel = my_data.vel + inst_accel * dt;
         my_data.pos = my_data.pos + my_data.vel * dt;
     }
-}
+}

src/simulation.rs

@@ -1,7 +1,5 @@
-extern crate num;
-
 use std::fmt;
-use num::{Float,Integer,NumCast};
+use num::{self,Float,Integer,NumCast};
 use vector::Vector2;
 use sim_elements::Simulable;
 
@@ -72,4 +70,4 @@ impl<T,U> fmt::Display for Simulation<T,U> where T: Float + fmt::Display, U: Int
         }
         Ok(())
     }
-}
+}

src/vector.rs

@@ -1,7 +1,5 @@
-extern crate num;
-
 use std::fmt;
-use num::Float;
+use num::{self,Float};
 use std::ops::{Add,Sub,Mul,Div};
 
 #[derive(Debug, Eq, PartialEq, Clone, Copy)]
@@ -106,4 +104,4 @@ mod tests{
     fn norm_test() {
         assert_eq!(Vector2::<f64> { x: 4., y: -3.}.norm(), 5_f64);
     }
-}
+}