Description: If x is not free in ph and ps , then it is not free in ( ph /\ ps ) . (Contributed by Mario Carneiro, 11-Aug-2016) (Proof shortened by Wolf Lammen, 13-Jan-2018) (Proof shortened by Wolf Lammen, 9-Oct-2021)

|- F/ x ph

|- F/ x ps

|- F/ x ( ph /\ ps )

|- ( T. -> F/ x ph )

|- ( T. -> F/ x ps )

|- ( T. -> F/ x ( ph /\ ps ) )