Unclear statement

Frank Yung-Fong Tang pointed out that the phrase "substituting every symbol x in the list L" on line 15 can be misleading. It should just say "substituting every symbol in the list L", or perhaps even more simply "substituting the symbols in the list L for any occurrence of the symbol s". Also, the following example (where the initial backquote is missing) with the replace operator -> is confusing because replacement has not yet been mentioned. It would be better to use an operator such as crossproduct that has already been introduced:

`[[a:b], b, x y z] denotes the same relation as [a:x | a:y | a:z].