How to match a word not following a defined pattern?

Question

I have the following text file:

1: This is a book.
2: Here is the book for you.
3: There are book.
4: You can read the book.
5: Is book good to read?

I want to find all occurrences of book not following a or the, that is, the book in Line 3,5 but not those on lines 1,2,4.

I tried to use the following search pattern:

[^a|the] book

however, this is only to check one character, but not the whole word.

Answer 1

The brackets are for chars. Use subpattern (parentheses) instead.

\%(a\|the\)\@3<! book

\%( ... \) --- a (unnumbered) submatch

a\|the --- "a" or "the"

\@3<! --- NO match behind (3 bytes lookback)