[PRD] Semantics of actions

Guys,

after re-reading my interpretation of Gary's proposal in terms of entailment (oh, ok: after reading it :-) I found out that my version of conditions 2 and 3 was much to strong: I think it should be "phi |=/= f", not "f |=/= phi" (same in condition 3, mutatis mutandi).

I made the correction on the wiki.

Cheers,

Christian