编写一个递归函数来重命名lambda演算中的项

def rename_term(term, mapping):
    if isinstance(term, str):  # 变量
        if term in mapping:
            return mapping[term]
        else:
            return term
    elif isinstance(term, list):  # 抽象或应用
        if term[0] == 'λ':  # 抽象
            new_var = term[1]
            new_body = rename_term(term[2], mapping)
            new_mapping = mapping.copy()
            new_mapping[new_var] = new_var  # 替换为新变量
            return ['λ', new_var, rename_term(new_body, new_mapping)]
        else:  # 应用
            new_left = rename_term(term[0], mapping)
            new_right = rename_term(term[1], mapping)
            return [new_left, new_right]
    else:
        return term

# 重命名 λx.x 为 λy.y
term1 = ['λ', 'x', 'x']
mapping1 = {'x': 'y'}
print(rename_term(term1, mapping1))  # ['λ', 'y', 'y']

# 重命名 (λx.x) y 为 (λy.y) y
term2 = [['λ', 'x', 'x'], 'y']
mapping2 = {'x': 'y'}
print(rename_term(term2, mapping2))  # [['λ', 'y', 'y'], 'y']