[Tex/LaTex] Custom Theorem Style

Question

I have a question that is similar to How can I make a custom theorem for a definition? and also to Custom theorem numbering italicized, but I'm not able to work out how to do it from these. My wish is the following:

define a custom theorem style so that the body of the text is slanted via \textsl{...} (not italicised via \textit{...}).

For example, I would like it to look like this.

\textbf{Theorem 1.1} (theorem name)\textbf{.} \textsl{Statement of theorem.}

This link https://en.wikibooks.org/wiki/LaTeX/Theorems#Custom_styles should also be helpful, but again I am unable to make it work myself.

Advice on how to do this would be most appreciated, thanks.

I'm using packages amsmath and ntheorem. I've no particular attachment to the package ntheorem: if changing to use a different package would make it easier, then I don't think this would mess up my other stuff.

Answer 1

(edited the answer after the OP provided more information about the desired appearance of the theorem-like environment.

I would like to suggest that you use the amsthm package and define a new theorem style, called sltheoremstyle in the example below.

\documentclass{article}

\usepackage{amsthm}
\newtheoremstyle{sltheorem}
{}                % Space above
{}                % Space below
{\slshape}        % Theorem body font % (default is "\upshape")
{}                % Indent amount
{\bfseries}       % Theorem head font % (default is \mdseries)
{.}               % Punctuation after theorem head % default: no punctuation
{ }               % Space after theorem head
{}                % Theorem head spec
\theoremstyle{sltheorem}
\newtheorem{theorem}{Theorem}

\begin{document}
\begin{theorem}[Wow] 
Hello World. 
\end{theorem}
\end{document}