Math & Science ⇒ Line spacing within theorems

[pengyau]

I am using a thesis template (using \documentstyle{thesis.sty}) to write my thesis, and thesis.sty contains the codes below.
My theorems have single line spacing while the main body has 1.5 line spacing.
How do I change the codes below to get 1.5 line spacing for my theorems? Thanks.

\def\mystretch{1.5} % One-and-a-half spacing hack
\def\ds@doublespace{\typeout{Double spaced}} % This is default
% So we do not read this style twice
\def\ds@singlespace{ % If he explicitly wants single spacing
\typeout{Single spaced}
\def\mystretch{1}}
\def\baselinestretch{\mystretch} % Double spacing hack


% new option: doublethm for double-spaced theorems
\def\ds@doublethm{\def\thesisthm
{\advance\@topsep \baselineskip % adjust back again (see \@trivlist)
\def\baselinestretch{\mystretch}%
\ifx\@currsize\normalsize\@normalsize\else\@currsize\fi
\advance\@topsep -\baselineskip}}
\def\thesisthm{} % single-spaced theorems by default


% modify LaTeX theorem environments to allow double-spaced option
\def\@begintheorem#1#2{\trivlist \thesisthm
\item[\hskip \labelsep{\bf #1\ #2}]\it}
\def\@opargbegintheorem#1#2#3{\trivlist \thesisthm
\item[\hskip \labelsep{\bf #1\ #2\ (#3)}]\it}

[pengyau]

Problem solved. I added in \thesisthm \it in all my theorems:

\begin{theorem} \label{theorem:Continuity}\thesisthm \it
Suppose that Assumptions 5 hold, and that Algorithm \ref{AlgoSD} terminates after $n$ iterations with ...
...
\end{theorem}

Adding \thesisthm makes my theorems 1.5 line spacing, but somehow the fonts change from italics to regular font, so need \it to make it italics again. There must be a better way to do this, but what the heck...