more accurate spacing, according to results seen in isar-ref (Appendix B), using 12pt or 10pt;

--- a/lib/texinputs/isabellesym.sty	Thu Mar 18 12:46:25 2021 +0100
+++ b/lib/texinputs/isabellesym.sty	Thu Mar 18 12:53:05 2021 +0100
@@ -206,12 +206,12 @@
 \newcommand{\isasymrceil}{\isamath{\rceil}}
 \newcommand{\isasymlfloor}{\isamath{\lfloor}}
 \newcommand{\isasymrfloor}{\isamath{\rfloor}}
-\newcommand{\isasymlparr}{\isamath{\mathopen{(\mkern-3mu\mid}}}
-\newcommand{\isasymrparr}{\isamath{\mathclose{\mid\mkern-3mu)}}}
+\newcommand{\isasymlparr}{\isamath{\mathopen{(\mkern-3.3mu\mid}}}
+\newcommand{\isasymrparr}{\isamath{\mathclose{\mid\mkern-3.3mu)}}}
 \newcommand{\isasymlbrakk}{\isamath{\mathopen{\lbrack\mkern-3mu\lbrack}}}
 \newcommand{\isasymrbrakk}{\isamath{\mathclose{\rbrack\mkern-3mu\rbrack}}}
-\newcommand{\isasymlbrace}{\isamath{\mathopen{\lbrace\mkern-4.5mu\mid}}}
-\newcommand{\isasymrbrace}{\isamath{\mathclose{\mid\mkern-4.5mu\rbrace}}}
+\newcommand{\isasymlbrace}{\isamath{\mathopen{\lbrace\mkern-4.3mu\mid}}}
+\newcommand{\isasymrbrace}{\isamath{\mathclose{\mid\mkern-4.3mu\rbrace}}}
 \newcommand{\isasymlblot}{\isamath{{\langle}\mkern -3.5mu{|}}}
 \newcommand{\isasymrblot}{\isamath{{|}\mkern -3.5mu{\rangle}}}
 \newcommand{\isasymguillemotleft}{\isatext{\flqq}}  %requires babel