theorem Th54: :: NOMIN_1:54

for a, a1, v, v1, v2 being object
for V, A being set st {v,v1,v2} c= V & {a,a1} c= A holds
ND_ex_4 (v,v1,v2,a,a1) in NDSS (V,(A \/ (NDSS (V,A))))