diff --git a/src/PropertiesEx.lagda b/src/PropertiesEx.lagda new file mode 100644 index 00000000..5e3d321c --- /dev/null +++ b/src/PropertiesEx.lagda @@ -0,0 +1,72 @@ +--- +title : "Properties Exercises" +layout : page +permalink : /PropertiesEx +--- + +\begin{code} +open import Naturals using (ℕ; suc; zero; _+_; _*_; _∸_) +open import Properties using (+-assoc; +-comm) +open import Relation.Binary.PropositionalEquality using (_≡_; refl; sym) + +\end{code} + +*Swapping terms* + +\begin{code} ++-swap : ∀ (m n p : ℕ) → m + (n + p) ≡ n + (m + p) ++-swap m n p rewrite sym (+-assoc m n p) | +-comm m n | +-assoc n m p = refl +\end{code} + +*Multiplication distributes over addition* + +\begin{code} +*-distrib-+ : ∀ (m n p : ℕ) → (m + n) * p ≡ m * p + n * p +*-distrib-+ zero n p = refl +*-distrib-+ (suc m) n p rewrite *-distrib-+ m n p | +-assoc p (m * p) (n * p) = refl +\end{code} + +*Multiplication is associative* + +\begin{code} +*-assoc : ∀ (m n p : ℕ) → (m * n) * p ≡ m * (n * p) +*-assoc zero n p = refl +*-assoc (suc m) n p rewrite *-distrib-+ n (m * n) p | *-assoc m n p = refl +\end{code} + +*Multiplications is commutative* + +\begin{code} +*-zero : ∀ (n : ℕ) → n * zero ≡ zero +*-zero zero = refl +*-zero (suc n) rewrite *-zero n = refl + ++-*-suc : ∀ (m n : ℕ) → n * suc m ≡ n + n * m ++-*-suc m zero = refl ++-*-suc m (suc n) rewrite +-*-suc m n | +-swap m n (n * m) = refl + +*-comm : ∀ (m n : ℕ) → m * n ≡ n * m +*-comm zero n rewrite *-zero n = refl +*-comm (suc m) n rewrite +-*-suc m n | *-comm m n = refl +\end{code} + +*Monus from zero* + +\begin{code} +0∸n≡0 : ∀ (n : ℕ) → zero ∸ n ≡ zero +0∸n≡0 zero = refl +0∸n≡0 (suc n) = refl +\end{code} + +The proof does not require induction. + +*Associativity of monus with addition* + +\begin{code} +∸-+-assoc : ∀ (m n p : ℕ) → (m ∸ n) ∸ p ≡ m ∸ (n + p) +∸-+-assoc m zero p = refl +∸-+-assoc zero (suc n) p rewrite 0∸n≡0 p = refl +∸-+-assoc (suc m) (suc n) p rewrite ∸-+-assoc m n p = refl +\end{code} + + diff --git a/src/RelationsEx.lagda b/src/RelationsEx.lagda new file mode 100644 index 00000000..fab5c79a --- /dev/null +++ b/src/RelationsEx.lagda @@ -0,0 +1,67 @@ +--- +title : "Relations Exercises" +layout : page +permalink : /RelationsEx +--- + +## Imports + +\begin{code} +open import Naturals using (ℕ; zero; suc; _+_; _*_; _∸_) +open import Relations using (_≤_; _<_; Trichotomy; even; odd) +open import Properties using (+-comm; +-identity; +-suc) +open import Relation.Binary.PropositionalEquality using (_≡_; refl; sym) +open import Data.Product using (∃; _,_) +open Trichotomy +open _<_ +open _≤_ +open even +open odd +\end{code} + +*Trichotomy* + +\begin{code} +trichotomy : ∀ (m n : ℕ) → Trichotomy m n +trichotomy zero zero = same refl +trichotomy zero (suc n) = less z