diff --git a/library/standard/bool.lean b/library/standard/bool.lean
index ddd203f68..aa44614da 100644
--- a/library/standard/bool.lean
+++ b/library/standard/bool.lean
@@ -116,6 +116,6 @@ using decidable
 theorem decidable_eq [instance] (a b : bool) : decidable (a = b)
 := bool_rec
     (bool_rec (inl (refl '0)) (inr b0_ne_b1) b)
-    (bool_rec (inr (not_eq_symm b0_ne_b1)) (inl (refl '1)) b)
+    (bool_rec (inr (ne_symm b0_ne_b1)) (inl (refl '1)) b)
     a
 end
diff --git a/library/standard/classical.lean b/library/standard/classical.lean
index ae4df841e..271fa6bb4 100644
--- a/library/standard/classical.lean
+++ b/library/standard/classical.lean
@@ -13,7 +13,7 @@ theorem case (P : Prop → Prop) (H1 : P true) (H2 : P false) (a : Prop) : P a
 
 theorem em (a : Prop) : a ∨ ¬a
 := or_elim (prop_complete a)
-     (assume Ht : a = true,  or_intro_left (¬ a) (eqt_elim Ht))
+     (assume Ht : a = true,  or_intro_left (¬a) (eqt_elim Ht))
      (assume Hf : a = false, or_intro_right a (eqf_elim Hf))
 
 theorem prop_complete_swapped (a : Prop) : a = false ∨ a = true
@@ -23,16 +23,16 @@ theorem prop_complete_swapped (a : Prop) : a = false ∨ a = true
         a
 
 theorem not_true : (¬true) = false
-:= have aux : ¬ (¬true) = true, from
+:= have aux : (¬true) ≠ true, from
      assume H : (¬true) = true,
        absurd_not_true (H⁻¹ ▸ trivial),
    resolve_right (prop_complete (¬true)) aux
 
 theorem not_false : (¬false) = true
-:= have aux : ¬ (¬false) = false, from
+:= have aux : (¬false) ≠ false, from
      assume H : (¬false) = false,
         H ▸ not_false_trivial,
-   resolve_right (prop_complete_swapped (¬ false)) aux
+   resolve_right (prop_complete_swapped (¬false)) aux
 
 theorem not_not_eq (a : Prop) : (¬¬a) = a
 := case (λ x, (¬¬x) = x)
@@ -83,41 +83,41 @@ theorem eq_id {A : Type} (a : A) : (a = a) = true
 theorem heq_id {A : Type} (a : A) : (a == a) = true
 := eqt_intro (hrefl a)
 
-theorem not_or (a b : Prop) : (¬ (a ∨ b)) = (¬ a ∧ ¬ b)
+theorem not_or (a b : Prop) : (¬(a ∨ b)) = (¬a ∧ ¬b)
 := propext
      (assume H, or_elim (em a)
-       (assume Ha, absurd_elim (¬ a ∧ ¬ b) (or_intro_left b Ha) H)
+       (assume Ha, absurd_elim (¬a ∧ ¬b) (or_intro_left b Ha) H)
        (assume Hna, or_elim (em b)
-         (assume Hb, absurd_elim (¬ a ∧ ¬ b) (or_intro_right a Hb) H)
+         (assume Hb, absurd_elim (¬a ∧ ¬b) (or_intro_right a Hb) H)
          (assume Hnb, and_intro Hna Hnb)))
-     (assume (H : ¬ a ∧ ¬ b) (N : a ∨ b),
+     (assume (H : ¬a ∧ ¬b) (N : a ∨ b),
        or_elim N
          (assume Ha, absurd Ha (and_elim_left H))
          (assume Hb, absurd Hb (and_elim_right H)))
 
-theorem not_and (a b : Prop) : (¬ (a ∧ b)) = (¬ a ∨ ¬ b)
+theorem not_and (a b : Prop) : (¬(a ∧ b)) = (¬a ∨ ¬b)
 := propext
      (assume H, or_elim (em a)
        (assume Ha, or_elim (em b)
-       (assume Hb, absurd_elim (¬ a ∨ ¬ b) (and_intro Ha Hb) H)
-         (assume Hnb, or_intro_right (¬ a) Hnb))
-         (assume Hna, or_intro_left (¬ b) Hna))
-     (assume (H : ¬ a ∨ ¬ b) (N : a ∧ b),
+       (assume Hb, absurd_elim (¬a ∨ ¬b) (and_intro Ha Hb) H)
+         (assume Hnb, or_intro_right (¬a) Hnb))
+         (assume Hna, or_intro_left (¬b) Hna))
+     (assume (H : ¬a ∨ ¬b) (N : a ∧ b),
        or_elim H
          (assume Hna, absurd (and_elim_left N) Hna)
          (assume Hnb, absurd (and_elim_right N) Hnb))
 
-theorem imp_or (a b : Prop) : (a → b) = (¬ a ∨ b)
+theorem imp_or (a b : Prop) : (a → b) = (¬a ∨ b)
 := propext
      (assume H : a → b, (or_elim (em a)
-       (assume Ha  : a,   or_intro_right (¬ a) (H Ha))
-       (assume Hna : ¬ a, or_intro_left b Hna)))
-     (assume (H : ¬ a ∨ b) (Ha : a),
+       (assume Ha  : a,   or_intro_right (¬a) (H Ha))
+       (assume Hna : ¬a, or_intro_left b Hna)))
+     (assume (H : ¬a ∨ b) (Ha : a),
        resolve_right H ((not_not_eq a)⁻¹ ◂ Ha))
 
-theorem not_implies (a b : Prop) : (¬ (a → b)) = (a ∧ ¬b)
-:= calc (¬ (a → b)) = (¬(¬a ∨ b)) : {imp_or a b}
-                 ... = (¬¬a ∧ ¬b)  : not_or (¬ a) b
+theorem not_implies (a b : Prop) : (¬(a → b)) = (a ∧ ¬b)
+:= calc (¬(a → b)) = (¬(¬a ∨ b)) : {imp_or a b}
+                 ... = (¬¬a ∧ ¬b)  : not_or (¬a) b
                  ... = (a ∧ ¬b)    : {not_not_eq a}
 
 theorem a_eq_not_a (a : Prop) : (a = ¬a) = false
@@ -125,7 +125,7 @@ theorem a_eq_not_a (a : Prop) : (a = ¬a) = false
      (assume H, or_elim (em a)
        (assume Ha, absurd Ha (H ▸ Ha))
        (assume Hna, absurd (H⁻¹ ▸ Hna) Hna))
-     (assume H, false_elim (a = ¬ a) H)
+     (assume H, false_elim (a = ¬a) H)
 
 theorem true_eq_false : (true = false) = false
 := not_true ▸ (a_eq_not_a true)
diff --git a/library/standard/diaconescu.lean b/library/standard/diaconescu.lean
index 730693fb6..5d338a18f 100644
--- a/library/standard/diaconescu.lean
+++ b/library/standard/diaconescu.lean
@@ -44,8 +44,8 @@ lemma p_implies_uv [private] : p → u = v
    show u = v, from
      Hpred ▸ (refl (epsilon (λ x, x = true ∨ p)))
 
-theorem em : p ∨ ¬ p
-:= have H : ¬(u = v) → ¬ p, from contrapos p_implies_uv,
+theorem em : p ∨ ¬p
+:= have H : ¬(u = v) → ¬p, from contrapos p_implies_uv,
    or_elim uv_implies_p
      (assume Hne : ¬(u = v), or_intro_right p (H Hne))
      (assume Hp : p, or_intro_left (¬p) Hp)
diff --git a/library/standard/logic.lean b/library/standard/logic.lean
index f15aa99d9..0bcd5c090 100644
--- a/library/standard/logic.lean
+++ b/library/standard/logic.lean
@@ -32,7 +32,7 @@ theorem not_not_intro {a : Prop} (Ha : a) : ¬¬a
 theorem mt {a b : Prop} (H1 : a → b) (H2 : ¬b) : ¬a
 := assume Ha : a, absurd (H1 Ha) H2
 
-theorem contrapos {a b : Prop} (H : a → b) : ¬ b → ¬ a
+theorem contrapos {a b : Prop} (H : a → b) : ¬b → ¬a
 := assume Hnb : ¬b, mt H Hnb
 
 theorem absurd_elim {a : Prop} (b : Prop) (H1 : a) (H2 : ¬a) : b
@@ -196,11 +196,8 @@ theorem a_neq_a_elim {A : Type} {a : A} (H : a ≠ a) : false
 theorem ne_irrefl {A : Type} {a : A} (H : a ≠ a) : false
 := H (refl a)
 
-theorem not_eq_symm {A : Type} {a b : A} (H : ¬ a = b) : ¬ b = a
-:= assume H1 : b = a, H (H1⁻¹)
-
 theorem ne_symm {A : Type} {a b : A} (H : a ≠ b) : b ≠ a
-:= not_eq_symm H
+:= assume H1 : b = a, H (H1⁻¹)
 
 theorem eq_ne_trans {A : Type} {a b c : A} (H1 : a = b) (H2 : b ≠ c) : a ≠ c
 := H1⁻¹ ▸ H2
@@ -301,14 +298,14 @@ theorem forall_not_exists {A : Type} {p : A → Prop} (H2 : ∀x, p x) : ¬∃x,
    obtain (w : A) (Hw : ¬p w), from H1,
    absurd (H2 w) Hw
 
-definition exists_unique {A : Type} (p : A → Prop) := ∃x, p x ∧ ∀y, y ≠ x → ¬ p y
+definition exists_unique {A : Type} (p : A → Prop) := ∃x, p x ∧ ∀y, y ≠ x → ¬p y
 
 notation `∃!` binders `,` r:(scoped P, exists_unique P) := r
 
-theorem exists_unique_intro {A : Type} {p : A → Prop} (w : A) (H1 : p w) (H2 : ∀y, y ≠ w → ¬ p y) : ∃!x, p x
+theorem exists_unique_intro {A : Type} {p : A → Prop} (w : A) (H1 : p w) (H2 : ∀y, y ≠ w → ¬p y) : ∃!x, p x
 := exists_intro w (and_intro H1 H2)
 
-theorem exists_unique_elim {A : Type} {p : A → Prop} {b : Prop} (H2 : ∃!x, p x) (H1 : ∀x, p x → (∀y, y ≠ x → ¬ p y) → b) : b
+theorem exists_unique_elim {A : Type} {p : A → Prop} {b : Prop} (H2 : ∃!x, p x) (H1 : ∀x, p x → (∀y, y ≠ x → ¬p y) → b) : b
 := obtain w Hw, from H2,
    H1 w (and_elim_left Hw) (and_elim_right Hw)
 
diff --git a/library/standard/wf.lean b/library/standard/wf.lean
index df0e4bc55..f56d3d30f 100644
--- a/library/standard/wf.lean
+++ b/library/standard/wf.lean
@@ -14,8 +14,8 @@ theorem wf_induction {A : Type} {R : A → A → Prop} {P : A → Prop} (Hwf : w
                      : ∀x, P x
 := by_contradiction (assume N : ¬∀x, P x,
      obtain (w : A) (Hw : ¬P w), from not_forall_exists N,
-       -- The main "trick" is to define Q x as ¬ P x.
-       -- Since R is well-founded, there must be a R-minimal element r s.t. Q r (which is ¬ P r)
+       -- The main "trick" is to define Q x as ¬P x.
+       -- Since R is well-founded, there must be a R-minimal element r s.t. Q r (which is ¬P r)
        let Q [inline] x := ¬P x in
        have Qw  : ∃w, Q w, from exists_intro w Hw,
        have Qwf : ∃min, Q min ∧ ∀b, R b min → ¬Q b, from Hwf Q Qw,
@@ -23,7 +23,7 @@ theorem wf_induction {A : Type} {R : A → A → Prop} {P : A → Prop} (Hwf : w
        -- Using the inductive hypothesis iH and Hr, we show P r, and derive the contradiction.
        have s1 : ∀b, R b r → P b, from
          take b : A, assume H : R b r,
-           -- We are using Hr to derive ¬ ¬ P b
+           -- We are using Hr to derive ¬¬P b
            not_not_elim (and_elim_right Hr b H),
        have s2 : P r,   from iH r s1,
        have s3 : ¬P r,  from and_elim_left Hr,