{
theoremstyle{change}
theoremheaderfont{scshape}
theorembodyfont{slshape}
newtheorem{thm}[defi]{Theorem.}
newtheorem{prop}[defi]{Proposition.}
newtheorem{lem}[defi]{Lemma.}
newtheorem{coro}[defi]{Corollary.}
}

begin{thm}
This is the first theorem.
end{thm}
This is a paragraph.
begin{thm}
This is the second theorem.
end{thm}
begin{thm}
This is the third theorem.
end{thm}