LookupError: NLTK was unable to find the prover9 file! （python自然语言处理章节10.2 Prover9示例报错）

平平无奇的清晨，冒着蒙蒙细雨，踏着破碎的枫叶，来到实验室开始Chapter10的学习~

一切都按部就班的进行着，突然，在运行以下示例时：

read_expr = nltk.sem.Expression.fromstring
lp = nltk.sem.Expression.fromstring
SnF = read_expr('SnF')
NotFnS = read_expr('-FnS')
R = read_expr('SnF -> -FnS')
prover = nltk.Prover9()
print(prover.prove(NotFnS, [SnF, R]))

遇到了一个错误：错误信息如下：

D:\Anaconda3\python.exe "E:/Python Practice/NLP/Chapter10.py"
Traceback (most recent call last):
  File "E:/Python Practice/NLP/Chapter10.py", line 45, in <module>
    print(prover.prove(NotFnS, [SnF, R]))
  File "D:\Anaconda3\lib\site-packages\nltk\inference\api.py", line 37, in prove
    return self._prove(goal, assumptions, verbose)[0]
  File "D:\Anaconda3\lib\site-packages\nltk\inference\prover9.py", line 330, in _prove
    self.prover9_input(goal, assumptions), verbose=verbose
  File "D:\Anaconda3\lib\site-packages\nltk\inference\prover9.py", line 351, in _call_prover9
    self._prover9_bin = self._find_binary("prover9", verbose)
  File "D:\Anaconda3\lib\site-packages\nltk\inference\prover9.py", line 184, in _find_binary
    verbose=verbose,
  File "D:\Anaconda3\lib\site-packages\nltk\internals.py", line 690, in find_binary
    name, path_to_bin, env_vars, searchpath, binary_names, url, verbose
  File "D:\Anaconda3\lib\site-packages\nltk\internals.py", line 674, in find_binary_iter
    path_to_bin or name, env_vars, searchpath, binary_names, url, verbose
  File "D:\Anaconda3\lib\site-packages\nltk\internals.py", line 632, in find_file_iter
    raise LookupError("\n\n%s\n%s\n%s" % (div, msg, div))
LookupError: 

===========================================================================
NLTK was unable to find the prover9 file!
Use software specific configuration paramaters or set the PROVER9 environment variable.

  Searched in:
    - /usr/local/bin/prover9
    - /usr/local/bin/prover9/bin
    - /usr/local/bin
    - /usr/bin
    - /usr/local/prover9
    - /usr/local/share/prover9

  For more information on prover9, see:
    <http://www.cs.unm.edu/~mccune/prover9/>
===========================================================================

Process finished with exit code 1

下面给出完整解决方法，参考文章附在文章结尾~

Step 1: 在官网下载Prover9

Prover9有GUI版本和Command Line版本。由于Command Line版本不提供Windows的版本，加之本人使用Windows系统，所以选择下载GUI版本的Prover9.地址为Prover9-Mace4 v05 (unm.edu)

就是下面这个Prover9-Mace4-v05-setup.exe 文件。