include "higher_order_defs/functions.ma".
-(* Magmas *)
+(* Semigroups *)
-record Magma : Type≝
+record PreSemiGroup : Type≝
{ carrier:> Type;
op: carrier → carrier → carrier
}.
-interpretation "magma operation" 'middot a b = (op _ a b).
-
-(* Semigroups *)
+interpretation "Semigroup operation" 'middot a b = (op ? a b).
-record isSemiGroup (M:Magma) : Prop≝
- { op_associative: associative ? (op M) }.
+record IsSemiGroup (S:PreSemiGroup) : Prop ≝
+ { op_is_associative: associative ? (op S) }.
record SemiGroup : Type≝
- { magma:> Magma;
- semigroup_properties:> isSemiGroup magma
+ { pre_semi_group:> PreSemiGroup;
+ is_semi_group :> IsSemiGroup pre_semi_group
}.
-
+
definition is_left_unit ≝
- λS:SemiGroup. λe:S. ∀x:S. e·x = x.
-
+ λS:PreSemiGroup. λe:S. ∀x:S. e·x = x.
+
definition is_right_unit ≝
- λS:SemiGroup. λe:S. ∀x:S. x·e = x.
+ λS:PreSemiGroup. λe:S. ∀x:S. x·e = x.
theorem is_left_unit_to_is_right_unit_to_eq:
- ∀S:SemiGroup. ∀e,e':S.
+ ∀S:PreSemiGroup. ∀e,e':S.
is_left_unit ? e → is_right_unit ? e' → e=e'.
intros;
rewrite < (H e');