No, functions from real numbers to real numbers are not propositional just because their domain and codomain (range) are not the set {T, F} of truth values.

The connection is made using characteristic functions. Given a subset S of some universal set U, the characteristic function of S, , is defined as follows.

(Usually 1 and 0 are used instead of T and F.) Then for any sets A, B, we have , and similarly for other set operations.