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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def create_definition(self, block_type, slug=None):
 """Make a definition, storing its block type."""

        prefix = "d"
        if slug:
            prefix += "_" + slug
        def_id = self._next_id(prefix)
        self._definitions[def_id] = block_type
        return def_id