Replaced all uses of 'thm' with 'Protected<thm0>'.
Piped the results of calls to certain parser-related functions (e.g., for operator overloading) into ExtCore.Choice.bindOrRaise so if the result of the function is an error (containing an exception), the exception will be raised.
Fixed the implementation of SPEC_VAR in bool.fs -- it had the wrong return type signature, and wasn't correctly propagating errors.