Concrete syntax involves both input syntax (for writing and editing, and subsequent parsing) and display format (for browsing on the screen, and publication on paper). The input syntax should preferably be easy to relate to the display format, and sufficiently readable for use in (plain-text) e-mail messages.
Section C.2 below provides a context-free grammar for the CASL input syntax. It has been derived systematically from the `abbreviated' abstract syntax grammar in Appendix B, except for the productions for mixfix formulae and terms. The context-free grammar is ambiguous; Section C.3 explains various precedence rules for disambiguation, and the intended grouping of mixfix formulae and terms. Section C.4 specifies the lexical symbols of the concrete syntax. Section C.5 shows how comments and various kinds of annotations may be written. Finally, Section C.6 introduces several annotations used to provide literal syntax for numbers, strings, and lists.