Fix two duplicated words and...

Fix two duplicated words and improve the phrasing of one sentence to
remove the appearance of a duplicate word.

website/learn/effective-elvish.md

@@ -191,7 +191,7 @@ output contains multiple lines, each line becomes one value:
 ▶ [lorem ipsum]
 ```
 
-Most Elvish builtin functions also work with with both byte and value inputs.
+Most Elvish builtin functions also work with both byte and value inputs.
 Similarly to output capture, they split their byte intput by newlines. For
 example:
 

website/learn/fundamentals.md

@@ -128,7 +128,7 @@ can just ask Elvish to recall it by pressing <span class="key">Up</span>:
 This will give you the last command you have run. However, it may have been a
 while when you have last run the `randint` command, and this will not give you
 what you need. You can either continue pressing <span class="key">Up</span>
-until you find the command, or you you can give Elvish a hint by typing some
+until you find the command, or you can give Elvish a hint by typing some
 characters from the command line you want, e.g. `ra`, before pressing <span
 class="key">Up</span>:
 

website/learn/unique-semantics.md

@@ -321,10 +321,10 @@ syntax tree, then **compile**s the syntax tree code to an internal
 representation, and finally **evaluate**s the just-generated internal
 representation.
 
-If any error happens during the first two phases, Elvish rejects the chunk
-without executing any of it. For instance, in Elvish unclosed parenthesis is a
-syntax error (error in the first parsing phase). The following code, when
-executed as a chunk, does nothing other than printing the parse error:
+If any error happens during the first two phases, Elvish rejects the
+chunk without executing any of it. For instance, in Elvish unclosed
+parenthesis is an error during the parsing phase. The following code,
+when executed as a chunk, does nothing other than printing the parse error:
 
 ```elvish-bad
 echo before