JavaScript must be enabled in order to use this site.Please enable JavaScript in your browser and refresh the page. Notation Conventions {x}* zero or more occurrences of x {x}+ one or more occurrences of x [x] zero or one occurrence of x x | y either x or y can appear, but not both of them x::= y x is defined by y <x> x is scalar ‘x x is symbol :x x is keyword (x) x is a list element Parent topic: Infix Expression Syntax