| MathQL.VVar s -> List.assoc s c.vvars
| MathQL.RefOf sexp -> List.map (fun (s,_) -> s) (exec_set_exp c sexp)
| MathQL.Fun (s, vexp) -> fun_ex s (exec_val_exp c vexp)
| MathQL.VVar s -> List.assoc s c.vvars
| MathQL.RefOf sexp -> List.map (fun (s,_) -> s) (exec_set_exp c sexp)
| MathQL.Fun (s, vexp) -> fun_ex s (exec_val_exp c vexp)