input: Write a python function to generate a summary of a given text.
  assert summarize("Natural language processing (NLP) is a field of artificial intelligence. NLP involves the interaction between computers and humans using the natural language. The ultimate goal of NLP is to enable computers to understand, interpret, and generate human language.") == "NLP involves the interaction between computers and humans using the natural language. The ultimate goal of NLP is to enable computers to understand, interpret, and generate human language."
  assert summarize("The quick brown fox jumps over the lazy dog. The lazy dog lies in the sun. The quick brown fox is very quick.") == "The quick brown fox jumps over the lazy dog. The quick brown fox is very quick."
  assert summarize("Python is a high-level programming language. Python is easy to learn. Python has a large community.") == "Python is a high-level programming language. Python is easy to learn. Python has a large community."
output: def summarize(text):
      sentences = text.split('. ')
      summary = []
      seen_sentences = set()
      
      for sentence in sentences:
          if sentence not in seen_sentences:
              summary.append(sentence)
              seen_sentences.add(sentence)
      
      return '. '.join(summary)