✅ Reference function (predicate calculus)

=== a function $I_V$ over a universe U, which clearly determines a value of truth for a given predicate formula A in a model M $M=<U,I>$ for V==

Defined as

$I_V(t)$ = - $I(t)$ if t is an 🙎 Individual constant - $V(t)$ if t is an 👤 Individual variable