improved \isachartilde for non-tt styles;

--- a/lib/texinputs/isabelle.sty	Thu Sep 21 15:58:13 2000 +0200
+++ b/lib/texinputs/isabelle.sty	Thu Sep 21 18:33:48 2000 +0200
@@ -131,6 +131,7 @@
 \renewcommand{\isacharbraceleft}{\emph{$\{$}}%
 \renewcommand{\isacharbar}{\emph{$\mid$}}%
 \renewcommand{\isacharbraceright}{\emph{$\}$}}%
+\renewcommand{\isachartilde}{\emph{${}^\sim$}}%
 }
 
 \newcommand{\isabellestylesl}{%