Error in a math expression

I have a problem with this expression:

$$n \geq \Bigg\lvert \bigcup_{l \leq |A_{i}| \leq 2l} |A_{i}| \Bigg\rvert \geq \sum_{i = 1}^{N_{l}}\Bigg\lvert A_{i} \Biggl \bigcup_{j =1}^{i-1} A_{j}\Biggr \Bigg\rvert$$


The report is:

* Local config file bblopts.cfg used * ("C:\Program Files\MiKTeX 2.9\tex\latex\00miktex\bblopts.cfg") ("C:\Program Files\MiKTeX 2.9\tex\generic\babel\italian.ldf" ("C:\Program Files\MiKTeX 2.9\tex\generic\babel\babel.def"))) (C:\Users\Stefano1\Desktop\Seminario\Seminario.aux) ("C:\Program Files\MiKTeX 2.9\tex\latex\amsfonts\umsa.fd") ("C:\Program Files\MiKTeX 2.9\tex\latex\amsfonts\umsb.fd") ("C:\Program Files\MiKTeX 2.9\tex\latex\base\omscmr.fd") [1{C:/ProgramData/MiKT eX/2.9/pdftex/config/pdftex.map}] [2] [3] [4] [5] [6] [7] [8] [9] ! Missing delimiter (. inserted). \bigcup@ l.296 ...}^{N_{l}}\Bigg\lvert A_{i} \Biggl \bigcup {j =1}^{i-1} A{j}\Biggr ...

?

I don't understand where is the error.

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Don't use . This is outdated. Use one \$ for inline or  for display. –  LaRiFaRi Apr 3 '14 at 9:11

Both after one \Biggl and one \Biggr a delimiter, such as \lvert or \rvert or any other (parenthessis, brace, dot), is missing. There's just a blank and another command following.

Compilable example code:

\documentclass{article}
\usepackage{amsmath,amssymb}
\begin{document}
$n \geq \Bigg\lvert \bigcup_{l \leq |A_{i}| \leq 2l} |A_{i}| \Bigg\rvert \geq \sum_{i = 1}^{N_{l}}\Bigg\lvert A_{i} \Biggl\lvert \bigcup_{j =1}^{i-1} A_{j}\Biggr\rvert \Bigg\rvert$
\end{document}


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As you just write, it would be great to have all \Bigg changed to \Biggl \Biggr and so on. –  Manuel Apr 3 '14 at 10:08
I think the expression would look even better if you replaced all \Bigg directives with \bigg: Just as it's not desirable in general, to surround a summation sign with upper and lower limits with parentheses that fully enclose the entire expression, the vertical bars generated by \Bigg seem oppresively tall; switching to \bigg[lr] will give less visual prominence to the fences, without creating any uncertainty as to what's being enclosed. –  Mico Apr 3 '14 at 11:12