I got so lost in the permutations that I think I will take a couple of days to list them all and then carefully construct a comprehensive test suite just to help me think about the rewrite. This will include attempted violations of the Cells discipline, such as setfing an input cell within an output method without wrapping it in a suitable macro that will defer the setf until propagation to dependencies is complete. This is a new discipline by the way. Really simplifies the code. Thx anyway, kt