How to git add -p a hunk?

after_edit

# Manual hunk edit mode -- see bottom for a quick guide.
@@ -1,13 +4,14 @@
 #[macro_use(azip)]
 extern crate ndarray;
 
 #[cfg(feature="tuple")]
 extern crate tuple;
 
-mod integrators;
+// mod integrators;
 mod steppers;
 mod ode;
 
 pub mod observers;
 
 // Re-exports
# ---
# To remove '-' lines, make them ' ' lines (context).
# To remove '+' lines, delete them.
# Lines starting with # will be removed.
# 
# If the patch applies cleanly, the edited hunk will immediately be
# marked for staging.
# If it does not apply cleanly, you will be given an opportunity to
# edit again.  If all lines of the hunk are removed, then the edit is
# aborted and the hunk is left unchanged.

error

error: patch failed: src/lib.rs:1
error: src/lib.rs: patch does not apply
Your edited hunk does not apply. Edit again (saying "no" discards!) [y/n]?

hunk

Stage this hunk [y,n,q,a,d,/,j,J,g,e,?]? n
@@ -1,13 +4,14 @@
 #[macro_use(azip)]
 extern crate ndarray;
 
 #[cfg(feature="tuple")]
 extern crate tuple;
 
-mod integrators;           <--- keep this
+// mod integrators;        <--- keep this
+// mod integrator_derive;  <--- remove this
 mod steppers;
 mod ode;
 
 pub mod observers;
 
 // Re-exports

pre_edit

# Manual hunk edit mode -- see bottom for a quick guide.
@@ -1,13 +4,14 @@
 #[macro_use(azip)]
 extern crate ndarray;
 
 #[cfg(feature="tuple")]
 extern crate tuple;
 
-mod integrators;
+// mod integrators;
+// mod integrator_derive;
 mod steppers;
 mod ode;
 
 pub mod observers;
 
 // Re-exports
# ---
# To remove '-' lines, make them ' ' lines (context).
# To remove '+' lines, delete them.
# Lines starting with # will be removed.
# 
# If the patch applies cleanly, the edited hunk will immediately be
# marked for staging.
# If it does not apply cleanly, you will be given an opportunity to
# edit again.  If all lines of the hunk are removed, then the edit is
# aborted and the hunk is left unchanged.