diff --git a/src/plfa/Isomorphism.lagda b/src/plfa/Isomorphism.lagda index 8858f512..0a517aa6 100644 --- a/src/plfa/Isomorphism.lagda +++ b/src/plfa/Isomorphism.lagda @@ -149,8 +149,8 @@ Let's unpack the definition. An isomorphism between sets `A` and `B` consists of four things: + A function `to` from `A` to `B`, + A function `from` from `B` back to `A`, -+ Evidence `from∘to` asserting that `from` is a *right-identity* for `to`, -+ Evidence `to∘from` asserting that `to` is a *left-identity* for `from`. ++ Evidence `from∘to` asserting that `from` is a *left-inverse* for `to`, ++ Evidence `to∘from` asserting that `from` is a *right-inverse* for `to`. In particular, the third asserts that `from ∘ to` is the identity, and the fourth that `to ∘ from` is the identity, hence the names. The declaration `open _≃_` makes available the names `to`, `from`, @@ -216,7 +216,7 @@ and `from` to be the identity function: In the above, `to` and `from` are both bound to identity functions, and `from∘to` and `to∘from` are both bound to functions that discard their argument and return `refl`. In this case, `refl` alone is an -adequate proof since for the left inverse, `to (from x)` +adequate proof since for the left inverse, `from (to x)` simplifies to `x`, and similarly for the right inverse. To show isomorphism is symmetric, we simply swap the roles of `to` @@ -326,8 +326,8 @@ record _≲_ (A B : Set) : Set where open _≲_ \end{code} It is the same as an isomorphism, save that it lacks the `to∘from` field. -Hence, we know that `from` is right-inverse to `to`, but not that `to` -is left-inverse to `from`. +Hence, we know that `from` is left-inverse to `to`, but not that `from` +is right-inverse to `to`. Embedding is reflexive and transitive, but not symmetric. The proofs are cut down versions of the similar proofs for isomorphism: