Abstract Two-sided conformally recurrent 4-dimensional self-dual spaces are considered. It is shown that such spaces are equipped with nonexpanding congruences of null strings. The general structure of weak nonexpanding hyperheavenly spaces is given. Finally, the general metrics of Petrov–Penrose type [ D ] ⊗ [ − ] spaces are presented.

中文翻译：

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两侧共形循环自对偶空间

摘要 考虑了两侧共形循环的四维自对偶空间。结果表明，这样的空间配备了空字符串的非扩展同余。给出了弱非膨胀超天空间的一般结构。最后，介绍了 Petrov-Penrose 类型 [ D ] ⊗ [ − ] 空间的一般度量。