The Sheffer stroke / NAND gate suffices to implement any function from 2^n -> 2. I'm looking for a similar universal basis for graph homomorphisms from Omega^n -> Omega, where Omega is the subgraph classifier with two vertices t, f and five edges in:t->t, out1:t->t, out2:t->f, out3:f->t, out4:f->f. There's obviously a finite set of operations that covers all graph homomorphisms from Omega^n to Omega, because the set of all operations of that form is finite. But how small can that set be? I'd be satisfied with a formula parametric in n, but surprised if it actually depends on n; I'd expect it to be a finite set of binary operations. -- Mike Stay - metaweta@gmail.com http://www.cs.auckland.ac.nz/~mike http://reperiendi.wordpress.com [For admin and other information see: http://www.mta.ca/~cat-dist/ ]