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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 find_deprecated_usages( schema: GraphQLSchema, ast: DocumentNode ) -> List[GraphQLError]: """Get a list of GraphQLError instances describing each deprecated use."""


    type_info = TypeInfo(schema)
    visitor = FindDeprecatedUsages(type_info)
    visit(ast, TypeInfoVisitor(type_info, visitor))
    return visitor.errors