SFI connects "filler" subjects "it" and "there" to invertible verbs in questions with s-v inversion: +SFI+ | | Is it likely that Jane will go Is there going to be a problem Both the use of "it" and "there" and the use of subject-verb inversion are highly constrained by post-processing (see "SF"; see "SI"). However, there is nothing especially problematic about SFI; SFI is to SF precisely as SI is to S.Grammar Documentation Page.