type binop = [ | `AndOp| `OrOp| `ImplOp| `EquivOp
]type cmpop = [ | `EqOp| `NeOp
]val string_of_bool : bool -> stringval string_of_unop : [< `NotOp ] -> stringval string_of_binop : [< `AndOp | `EquivOp | `ImplOp | `OrOp ] -> stringval string_of_cmpop : [< `EqOp | `NeOp ] -> string