首楞嚴義疏注經 2.233

2.233

方器中空若定方者，除去方器別著圓器，此處虛空應無圓相。若言虛空不定方者，顯是方器無方虛空。

If the space in a square vessel were definitely square, then upon removing the square vessel and placing another round vessel there, the space in that location should have no round appearance. If one says that space is not definitely square, then clearly in a square vessel there is no square space.