When TRACE function returns a set of { Ψ k , Φ k }, all ψ ∈ Ψ k are aligned with phrases in the source and their inside probabilities are stored in A.
we can compute the inside probability for each Ψ k , Φ k , which is stored in A to-Source: Relying on team spirit, expedition members defeated difficulties  Although we have discussed using trees for clarity, the alignment is conducted on forests.