Found:

INFL

SYNTAX: functional head containing (in English) auxiliary verbs and/or tense and/or agreement features. Also written as I (I⁰). More recently, INFL has been reinterpreted as a conflation of two separate heads AGR (agreement) and T (tense).

LIT.	Chomsky, N. (1991) Chomsky, N. (1981) Pollock, J.-Y. (1989)