A Plan is a finite partially ordered set of service calls in states {S₁,... S_i,...S_n}
where
where service W_l is called in state S_l and

• The values of the instantiations of each property in the propositions in E(W_i), including Outputs,
  are used for the the same properties in the call of each of the properties
  in the propositions of P(W_j), including Inputs, and
• (S_i < S_j) ∧ ( ∃ _k | S_i <S_k < S_j => P^p(W_j) ∉ E^p(W_k) ,
• Now is the time to refine this last condition.