 
Summary: Epilogue: Formal and informal
correctness proofs
I would like to conclude with a note about the origin and motivation for this
work. When I turned towards computer science my coworkers were Menachem
Magidor and Shai BenDavid, and the first questions we studied were about
mutual exclusion protocols, and issues envisaged by L. Lamport concerning the
concept of global time. Most of our results are not suitable for an introductory
text, but their influence is evident, and the place of system executions in my
work can be traced back to that period and is a testimony to the influence of
Lamport's [20] on my work. At that time I was interested in atomic register
problems, and it was expressly in order to prove the correctness of the protocol
found in [1] that the usage of higherlevel properties developed.
The quest for a mathematical framework within which properties of protocols
could be proven has been a central motivation for the work presented here. To
describe this motivation I would like to quote from a work written with Shai
BenDavid. 1 Usually it is not good manners to quote from your own papers, but
this one was never published, so that I feel like honoring a neglected friend.
Proofs in mathematics can have different aspects, but two are
prominent. The first one, of course, is that a proof is used to
validate a statementto establish a theorem. Yet there might be
