for V being free finite-rank Z_Module
for b1, b2 being OrdBasis of V
for f being bilinear-Form of V,V st 0 < rank V holds
BilinearM (f,b2,b2) = ((AutMt ((id V),b2,b1)) * (BilinearM (f,b1,b1))) * ((AutMt ((id V),b2,b1)) @)