Three Non-Collinear Planes have One Point in Common

Theorem
Three planes which are not collinear have exactly one point in all three planes.

Proof
Let $A$, $B$ and $C$ be the three planes in question.

From Two Planes have Line in Common, $A$ and $B$ share a line, $p$ say.

From Propositions of Incidence: Plane and Line, $p$ meets $C$ in one point.