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.