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Showing content from https://agda.github.io/agda-stdlib/master/Algebra.Module.Properties.Semimodule.html below:

Algebra.Module.Properties.Semimodule

Algebra.Module.Properties.Semimodule
------------------------------------------------------------------------
-- The Agda standard library
--
-- Properties of semimodules.
------------------------------------------------------------------------

{-# OPTIONS --cubical-compatible --safe #-}

open import Algebra.Bundles        using (CommutativeSemiring)
open import Algebra.Module.Bundles using (Semimodule)
open import Level                  using (Level)

module Algebra.Module.Properties.Semimodule
  {r ℓr m ℓm : Level}
  {semiring  : CommutativeSemiring r ℓr}
  (semimod   : Semimodule semiring m ℓm)
  where

open CommutativeSemiring semiring
open Semimodule          semimod
open import Relation.Binary.Reasoning.Setoid ≈ᴹ-setoid
open import Relation.Nullary.Negation using (contraposition)

x≈0⇒x*y≈0 :  {x y}  x  0#  x *ₗ y ≈ᴹ 0ᴹ
x≈0⇒x*y≈0 {x} {y} x≈0 = begin
  x  *ₗ y ≈⟨ *ₗ-congʳ x≈0 
  0# *ₗ y ≈⟨ *ₗ-zeroˡ y 
  0ᴹ      

y≈0⇒x*y≈0 :  {x y}  y ≈ᴹ 0ᴹ  x *ₗ y ≈ᴹ 0ᴹ
y≈0⇒x*y≈0 {x} {y} y≈0 = begin
  x *ₗ y  ≈⟨ *ₗ-congˡ y≈0 
  x *ₗ 0ᴹ ≈⟨ *ₗ-zeroʳ x 
  0ᴹ      

x*y≉0⇒x≉0 :  {x y}  x *ₗ y ≉ᴹ 0ᴹ  x  0#
x*y≉0⇒x≉0 = contraposition x≈0⇒x*y≈0

x*y≉0⇒y≉0 :  {x y}  x *ₗ y ≉ᴹ 0ᴹ  y ≉ᴹ 0ᴹ
x*y≉0⇒y≉0 = contraposition y≈0⇒x*y≈0

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