You wrote:

There are two problems:

(1) Apparently, there is some "option clash" when I use the amsart
document class.

The reason there's an "option clash" is that the `amsmath`

package is already loaded by the `amsart`

document class; hence, it shouldn't be loaded a second time with options that weren't already specified the first time the package was loaded (in the present case, at the `\documentclass`

stage). To activate the options `nosumlimits`

and `intlimits`

, you must load them via the `\documentclass`

command:

```
\documentclass[nosumlimits,intlimits]{amsart}
```

(2) There is no "clash" with the article document class. But the
output does not agree with the stated outcome of the manual.

Recall that TeX has two math styles: "text style", also called "inline style", and "display style". The following MWE illustrates (i) the differences in the sizes of the integral signs in the two math styles and (ii) the effects that the commands `\int\limits`

and `\int\nolimits`

have in each of the two styles. Observe that the `amsmath`

package is loaded with the `intlimits`

option. As you can see from the ouput of this code, when in *inline math* style one must state `\int\limits`

explicily in order to get the limits set below/above the integral symbol even if the `intlimits`

option was specified. Conversely, when in *display math* style, the limits will always be set below/above the integral sign *unless* one specifies `\int\nolimits`

.

```
\documentclass{article}
\usepackage[intlimits]{amsmath}
\usepackage{booktabs,tabularx}
\newcolumntype{C}{X}
\begin{document}
Package \texttt{amsmath} loaded with \texttt{intlimits} option.
\begin{tabularx}{\textwidth}{@{}l *{3}{>{\raggedright\arraybackslash}X} @{}}
\toprule
Math style
& explicitly require side-set limits
& no explicit directive for positioning of limits
& explicitly require below\slash above limits\\ \midrule
Inline
& $\int\nolimits_0^1 f(x)\,dx$
& $\int_0^1 f(x)\,dx$
& $\int\limits _0^1 f(x)\,dx$ \\[3ex]
Display
& $\displaystyle \int\nolimits_0^1 f(x)\,dx$
& $\displaystyle \int_0^1 f(x)\,dx$
& $\displaystyle \int\limits _0^1 f(x)\,dx$ \\ \bottomrule
\end{tabularx}
\end{document}
```

Of course, when in inline math mode, one usually does *not* want the limits of integration to be typeset below/above the integral symbol, because one generally wants to keep the size of the math expressions compact so that the gaps between successive lines don't become too large. In contrast, in equations that are offset or displayed on a line by themselves, typesetting the limits of integration below and above the integral symbol may be a good choice, especially if the integrand is "large", e.g., if it contains a fractional expression.

## Best Answer

`\genfrac`

won't produce a line if the third argument (which control the thickness of the rule) is set to`0pt`

; the syntax for`\genfrac`

isA little example: