Formula for the Search Space as a Union of Complete Sequences

In a sequence generation process, a sequence is considered 'complete' if it ends with a special ⟨EOS⟩ token. At a given step i, the set of all candidate sequences is Yi = {('The', 'cat', 'sat'), ('The', 'cat', 'slept', '⟨EOS⟩'), ('The', 'dog'), ('The', 'dog', 'barked', '⟨EOS⟩')}. If Ψ(Yi) represents the subset of sequences in Yi that are complete, which of the following correctly identifies Ψ(Yi)?

Defining the Set of Complete Sequences

In a step-wise sequence generation process, the set denoted by Ψ(Yi) contains all candidate sequences from step i that will be expanded to create new, longer sequences in the subsequent step.