Check out the dates on these papers -
https://ieeexplore.ieee.org/abstract/document/286901 < 1994
https://ieeexplore.ieee.org/abstract/document/344783 < 1993
https://link.springer.com/article/10.1007/BF00337115 < 1986
Check out the dates on these papers -
https://ieeexplore.ieee.org/abstract/document/286901 < 1994
https://ieeexplore.ieee.org/abstract/document/344783 < 1993
https://link.springer.com/article/10.1007/BF00337115 < 1986