  The safe-consensus task was introduced by Afek, Gafni and Lieber (DISC' 09)
as a weakening of the classic consensus. When there is concurrency, the
consensus output can be arbitrary, not even the input of any process. They
showed that safe-consensus is equivalent to consensus, in a wait-free system.
We study the solvability of consensus in three shared memory iterated models
extended with the power of safe-consensus black boxes. In the first iterated
model, for the $i$-th iteration, the processes write to memory, then they
snapshot it and finally they invoke safe-consensus boxes. We prove that in this
model, consensus cannot be implemented. In a second iterated model, processes
first invoke safe-consensus, then they write to memory and finally they
snapshot it. We show that this model is equivalent to the previous model and
thus consensus cannot be implemented. In the last iterated model, processes
write to the memory, invoke safe-consensus boxes and finally they snapshot the
memory. We show that in this model, any wait-free implementation of consensus
requires $\binom{n}{2}$ safe-consensus black-boxes and this bound is tight.
