theorem Th19: :: MIDSP_3:19

for n being Nat
for RAS being non empty MidSp-like ReperAlgebraStr over n + 2
for W being ATLAS of RAS holds
( RAS is being_invariance iff for a, b being Point of RAS
for x being Tuple of (n + 1),W holds Phi (a,x) = Phi (b,x) )