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SFI
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.