# Subscripts actually under a union of sets sign

#### Peter

##### Well-known member
MHB Site Helper
I recently made a post on Linear and Abstract Algebra and used the following symbol

$$\displaystyle {\bigcup}_{\Omega \subseteq \Gamma , | \Omega | \lt \infty}$$

However, I really wanted (for neatness and clarity) to have the term $$\displaystyle {\Omega \subseteq \Gamma , | \Omega | \lt \infty}$$ actually under the set union symbol as in the commutative algebra text by R.Y. Sharp - see attachment page 7 exercise 1.12.

Peter

#### Jameson

Staff member
I recently made a post on Linear and Abstract Algebra and used the following symbol

$$\displaystyle {\bigcup}_{\Omega \subseteq \Gamma , | \Omega | \lt \infty}$$

However, I really wanted (for neatness and clarity) to have the term $$\displaystyle {\Omega \subseteq \Gamma , | \Omega | \lt \infty}$$ actually under the set union symbol as in the commutative algebra text by R.Y. Sharp - see attachment page 7 exercise 1.12.

Peter
Hmm, let's see if this works...

$$\displaystyle \underset{\Omega \subseteq \Gamma , | \Omega | \lt \infty}{{\bigcup}}$$

It does! Here you go:

\underset{\Omega \subseteq \Gamma , | \Omega | \lt \infty}{{\bigcup}}

#### Peter

##### Well-known member
MHB Site Helper
Hmm, let's see if this works...

$$\displaystyle \underset{\Omega \subseteq \Gamma , | \Omega | \lt \infty}{{\bigcup}}$$

It does! Here you go:

\underset{\Omega \subseteq \Gamma , | \Omega | \lt \infty}{{\bigcup}}
Thanks Jameson, appreciate the help

Peter

#### Evgeny.Makarov

MHB Math Scholar
If subscripts and superscripts of big operators are typeset below and above the operator, they are referred to as limits. Whether TeX uses limits depends on whether the formula is in display style (limits are used) or text style (normal sub- and superscipts are used). By default, inline formulas beginning with $$and  are typeset in text style, while those beginning with \[ and  use display style. (Note that  is deprecated, at least in PDF documents.) The tags $...$ on this site apparently create an inline formula but use display style. The style determines many other parameters besides whether to use limits; most noticeable are the size of operators and fractions. You used the $tag, so the formula is in display style, but you enclosed \bigcup in curly braces. This turned it into a generic subformula and TeX did not take into account that inside is a big operator, which treats subscripts in a special way. That's why the subscript was not made into a limit. Without changing the position of a formula (display or inline), its style can be modified using \displaystyle and \textstyle commands. Independently of this, you can type \limits or \nolimits immediately after a big operator to direct TeX to use limits or not. Edit: See this thread for examples of formulas in display style and text style. Edit 2: The info above relates to big operators (in TeX terminology) like \bigcup. The command \underset can be used in other contexts. Last edited: #### Jameson ##### Administrator Staff member Interesting and good to know, Evgeny.Makarov! I'll test this out. Here is without putting \bigcup in curly brackets: \(\displaystyle \bigcup_{\text{testing if this works}}$$ And here is with curly brackets: $$\displaystyle {\bigcup}_{\text{testing if this works}}$$ Yep, this way is much faster than my solution. #### Peter ##### Well-known member MHB Site Helper If subscripts and superscripts of big operators are typeset below and above the operator, they are referred to as limits. Whether TeX uses limits depends on whether the formula is in display style (limits are used) or text style (normal sub- and superscipts are used). By default, inline formulas beginning with \( and  are typeset in text style, while those beginning with \[ and  use display style. (Note that  is deprecated, at least in PDF documents.) The tags [math]...$ on this site apparently create an inline formula but use display style. The style determines many other parameters besides whether to use limits; most noticeable are the size of operators and fractions.

You used the [math] tag, so the formula is in display style, but you enclosed \bigcup in curly braces. This turned it into a generic subformula and TeX did not take into account that inside is a big operator, which treats subscripts in a special way. That's why the subscript was not made into a limit.

Without changing the position of a formula (display or inline), its style can be modified using \displaystyle and \textstyle commands. Independently of this, you can type \limits or \nolimits immediately after a big operator to direct TeX to use limits or not.

Edit: See this thread for examples of formulas in display style and text style.

Edit 2: The info above relates to big operators (in TeX terminology) like \bigcup. The command \underset can be used in other contexts.
Thanks Evgeny

A most informative post!

Peter