Observability relations and observability don't cares

The observability relation O(x,z) or the Boolean relation provides a description of all the flexibility one has in implementing a Boolean network N. The authors represent and use this flexibility in a logic synthesis system by adding a single output node to the Boolean network N. The node function for the new node is O(x,z). The newly constructed network N' (called the observability network) has only one output and computes 1 for every input x. It is shown that the observability don't cares (ODCs) for a node y/sub i/ in N' provide the maximum flexibility for implementing y/sub i/ and subsume the flexibility obtained for y/sub i/ in N even with don't cares provided at each output. This gives rise to new methods for computing complete ODCs for N' and hence for N.<<ETX>>