The Algebraic Criteria for the All┐delay Stability of Two┐dimensional Degenerate Differential Systems with Delay 
蒋 威, 郑祖庥
The Algebraic Criteria for the All┐delay Stability of Two┐dimensional Degenerate Differential Systems with Delay 
Jiang Wei, Zheng Zuxiu
数学季刊 . 1998, (1): 87 -93 .