\def\lbrace{{{\setcount0=`}}} \def\rbrace{{\setcount0=`{}}} \tracingcommands1 \tracingonline1 \tracingmacros1 \hbox\lbrace x\rbrace \showlists \halign{a#b&c#d\cr \lbrace&\rbrace\cr \rbrace&\lbrace\cr \showlists