* \isabellestyle{it} produces near math mode output;
* settings: smart setup of canonical ML_HOME, ISABELLE_INTERFACE, XSYMBOL_HOME;
types 'v binop = 'v => 'v => 'v
datatype ('a,'v) expr = Cex 'v
| Vex 'a
| Bex ('v binop) (('a,'v) expr) (('a,'v) expr)