diff --git a/library/standard/congruence.lean b/library/standard/congruence.lean
index 08a6ce007..24b70f712 100644
--- a/library/standard/congruence.lean
+++ b/library/standard/congruence.lean
@@ -9,59 +9,137 @@ import function
 
 using function
 
-namespace congruence
-
--- TODO: delete this
-axiom sorry {P : Prop} : P
+namespace congr
 
 -- TODO: move this somewhere else
 abbreviation reflexive {T : Type} (R : T → T → Type) : Prop := ∀x, R x x
 
-section
 
-parameters {T1 : Type} {T2 : Type} (R1 : T1 → T1 → Prop) (R2 : T2 → T2 → Prop) (f : T1 → T2)
+-- Congruence classes for unary and binary functions
+-- -------------------------------------------------
 
-definition congruence : Prop := ∀x y : T1, R1 x y → R2 (f x) (f y)
+-- TODO: call this 'class', so outside it is congruence.class
+inductive struc {T1 : Type} (R1 : T1 → T1 → Prop) {T2 : Type} (R2 : T2 → T2 → Prop)
+    (f : T1 → T2) : Prop :=
+| mk : (∀x y : T1, R1 x y → R2 (f x) (f y)) → struc R1 R2 f
 
-theorem congr_app {H1 : congruence} {x y : T1} (H2 : R1 x y) : R2 (f x) (f y) := H1 x y H2
+abbreviation app {T1 : Type} {R1 : T1 → T1 → Prop} {T2 : Type} {R2 : T2 → T2 → Prop}
+    {f : T1 → T2} (C : struc R1 R2 f) ⦃x y : T1⦄ : R1 x y → R2 (f x) (f y) :=
+struc_rec id C x y
 
-end
+-- to trigger class inference
+theorem infer {T1 : Type} (R1 : T1 → T1 → Prop) {T2 : Type} (R2 : T2 → T2 → Prop)
+    (f : T1 → T2) {C : struc R1 R2 f} ⦃x y : T1⦄ : R1 x y → R2 (f x) (f y) :=
+struc_rec id C x y
 
-theorem congr_trivial [instance] {T : Type} (R : T → T → Prop) : congruence R R id := take x y H, H
+-- for binary functions
+inductive struc2 {T1 : Type}  (R1 : T1 → T1 → Prop) {T2 : Type} (R2 : T2 → T2 → Prop)
+    {T3 : Type} (R3 : T3 → T3 → Prop) (f : T1 → T2 → T3) : Prop :=
+| mk2 : (∀(x1 y1 : T1) (x2 y2 : T2), R1 x1 y1 → R2 x2 y2 → R3 (f x1 x2) (f y1 y2)) →
+    struc2 R1 R2 R3 f
 
-theorem congr_const {T2 : Type} (R2 : T2 → T2 → Prop) (H : reflexive R2) :
-  ∀(T1 : Type) (R1 : T1 → T1 → Prop) (c : T2), congruence R1 R2 (const T1 c) :=
-take T1 R1 c x y H1, H c
+abbreviation app2 {T1 : Type} {R1 : T1 → T1 → Prop} {T2 : Type} {R2 : T2 → T2 → Prop}
+    {T3 : Type} {R3 : T3 → T3 → Prop}
+    {f : T1 → T2 → T3} (C : struc2 R1 R2 R3 f) ⦃x1 y1 : T1⦄ ⦃x2 y2 : T2⦄
+  : R1 x1 y1 → R2 x2 y2 → R3 (f x1 x2) (f y1 y2) :=
+struc2_rec id C x1 y1 x2 y2
 
-theorem congr_const_iff [instance] (T1 : Type) (R1 : T1 → T1 → Prop) (c : Prop) :
-  congruence R1 iff (const T1 c) := congr_const iff iff_refl T1 R1 c
 
-theorem congr_and [instance] (T : Type) (R : T → T → Prop) (f1 f2 : T → Prop)
-    (H1 : congruence R iff f1) (H2 : congruence R iff f2) :
-  congruence R iff (λx, f1 x ∧ f2 x) := sorry
+-- General tools to build instances
+-- --------------------------------
 
-theorem congr_or [instance] (T : Type) (R : T → T → Prop) (f1 f2 : T → Prop)
-    (H1 : congruence R iff f1) (H2 : congruence R iff f2) :
-  congruence R iff (λx, f1 x ∨ f2 x) := sorry
+theorem compose
+    {T2 : Type} {R2 : T2 → T2 → Prop}
+    {T3 : Type} {R3 : T3 → T3 → Prop}
+    {g : T2 → T3} (C2 : congr.struc R2 R3 g)
+    {{T1 : Type}} {R1 : T1 → T1 → Prop}
+    {f : T1 → T2} (C1 : congr.struc R1 R2 f) :
+  congr.struc R1 R3 (λx, g (f x)) := mk (take x1 x2 H, app C2 (app C1 H))
 
-theorem congr_implies [instance] (T : Type) (R : T → T → Prop) (f1 f2 : T → Prop)
-    (H1 : congruence R iff f1) (H2 : congruence R iff f2) :
-  congruence R iff (λx, f1 x → f2 x) := sorry
+theorem compose21
+    {T2 : Type} {R2 : T2 → T2 → Prop}
+    {T3 : Type} {R3 : T3 → T3 → Prop}
+    {T4 : Type} {R4 : T4 → T4 → Prop}
+    {g : T2 → T3 → T4} (C3 : congr.struc2 R2 R3 R4 g)
+    ⦃T1 : Type⦄ {R1 : T1 → T1 → Prop}
+    {f1 : T1 → T2} (C1 : congr.struc R1 R2 f1)
+    {f2 : T1 → T3} (C2 : congr.struc R1 R3 f2) :
+  congr.struc R1 R4 (λx, g (f1 x) (f2 x)) := mk (take x1 x2 H, app2 C3 (app C1 H) (app C2 H))
 
-theorem congr_iff [instance] (T : Type) (R : T → T → Prop) (f1 f2 : T → Prop)
-    (H1 : congruence R iff f1) (H2 : congruence R iff f2) :
-  congruence R iff (λx, f1 x ↔ f2 x) := sorry
+theorem trivial [instance] {T : Type} (R : T → T → Prop) : struc R R id :=
+mk (take x y H, H)
 
-theorem congr_not [instance] (T : Type) (R : T → T → Prop) (f : T → Prop)
-    (H : congruence R iff f) :
-  congruence R iff (λx, ¬ f x) := sorry
+theorem const {T2 : Type} (R2 : T2 → T2 → Prop) (H : reflexive R2) :
+  ∀(T1 : Type) (R1 : T1 → T1 → Prop) (c : T2), struc R1 R2 (function.const T1 c) :=
+take T1 R1 c, mk (take x y H1, H c)
+
+-- instances for logic
+-- -------------------
+
+-- TODO: swap order for and_elim?
+
+abbreviation imp (a b : Prop) : Prop := a → b
+
+theorem and_imp_and {a b c d : Prop} (H1 : a ∧ b) (H2 : a → c) (H3 : b → d) : c ∧ d :=
+and_elim (assume Ha : a, assume Hb : b, and_intro (H2 Ha) (H3 Hb)) H1
+
+theorem imp_and_left {a b c : Prop} (H1 : a ∧ c) (H : a → b) : b ∧ c :=
+and_elim (assume Ha : a, assume Hc : c, and_intro (H Ha) Hc) H1
+
+theorem imp_and_right {a b c : Prop} (H1 : c ∧ a) (H : a → b) : c ∧ b :=
+and_elim (assume Hc : c, assume Ha : a, and_intro Hc (H Ha)) H1
+
+theorem congr_not : congr.struc iff iff not :=
+congr.mk
+  (take a b,
+    assume H : a ↔ b, iff_intro
+      (assume H1 : ¬a, assume H2 : b, H1 (iff_elim_right H H2))
+      (assume H1 : ¬b, assume H2 : a, H1 (iff_elim_left H H2)))
+
+theorem congr_and : congr.struc2 iff iff iff and :=
+congr.mk2
+  (take a1 b1 a2 b2,
+    assume H1 : a1 ↔ b1, assume H2 : a2 ↔ b2,
+    iff_intro
+      (assume H3 : a1 ∧ a2, and_imp_and H3 (iff_elim_left H1) (iff_elim_left H2))
+      (assume H3 : b1 ∧ b2, and_imp_and H3 (iff_elim_right H1) (iff_elim_right H2)))
+
+theorem congr_or : congr.struc2 iff iff iff or :=
+congr.mk2
+  (take a1 b1 a2 b2,
+    assume H1 : a1 ↔ b1, assume H2 : a2 ↔ b2,
+    iff_intro
+      (assume H3 : a1 ∨ a2, or_imp_or H3 (iff_elim_left H1) (iff_elim_left H2))
+      (assume H3 : b1 ∨ b2, or_imp_or H3 (iff_elim_right H1) (iff_elim_right H2)))
+
+theorem congr_imp : congr.struc2 iff iff iff imp :=
+congr.mk2
+  (take a1 b1 a2 b2,
+    assume H1 : a1 ↔ b1, assume H2 : a2 ↔ b2,
+    iff_intro
+      (assume H3 : a1 → a2, assume Hb1 : b1, iff_elim_left H2 (H3 ((iff_elim_right H1) Hb1)))
+      (assume H3 : b1 → b2, assume Ha1 : a1, iff_elim_right H2 (H3 ((iff_elim_left H1) Ha1))))
+
+theorem congr_iff : congr.struc2 iff iff iff iff :=
+congr.mk2
+  (take a1 b1 a2 b2,
+    assume H1 : a1 ↔ b1, assume H2 : a2 ↔ b2,
+    iff_intro
+      (assume H3 : a1 ↔ a2, iff_trans (iff_symm H1) (iff_trans H3 H2))
+      (assume H3 : b1 ↔ b2, iff_trans H1 (iff_trans H3 (iff_symm H2))))
+
+theorem congr_const_iff [instance] := congr.const iff iff_refl
+theorem congr_not_compose [instance] := congr.compose congr_not
+theorem congr_and_compose [instance] := congr.compose21 congr_and
+theorem congr_or_compose [instance] := congr.compose21 congr_or
+theorem congr_implies_compose [instance] := congr.compose21 congr_imp
+theorem congr_iff_compose [instance] := congr.compose21 congr_iff
+
+theorem subst_iff {T : Type} {R : T → T → Prop} {P : T → Prop} {C : struc R iff P}
+  {a b : T} (H : R a b) (H1 : P a) : P b := iff_mp_left (app C H) H1
 
 theorem test1 (a b c d e : Prop) (H1 : a ↔ b) : (a ∨ c → ¬(d → a)) ↔ (b ∨ c → ¬(d → b)) :=
-  congr_app iff iff _ H1
-
-theorem subst_iff {T : Type} {R : T → T → Prop} {P : T → Prop} {Hcongr : congruence R iff P}
-    {a b : T} (H : R a b) (H1 : P a) : P b :=
-iff_mp_left (@congr_app _ _ R iff P Hcongr _ _ H) H1
+congr.infer iff iff _ H1
 
 theorem test2 (a b c d e : Prop) (H1 : a ↔ b) (H2 : a ∨ c → ¬(d → a)) : b ∨ c → ¬(d → b) :=
 subst_iff H1 H2