Every unitary operator U : X → X is normal. b) A matrix is unitary if and only if it is invertible. c) If two matrices are unitarily equivalent, then they are also similar. d) The sum of self-adjoint operators is self-adjoint. e) The adjoint of a unitary operator is unitary. f) The adjoint of a normal operator is normal. g) If all eigenvalues of a linear operator are 1, then the operator must be unitary or orthogonal. h) If all eigenvalues of a normal operator are 1, then the operator is identity. i) A linear operator may preserve norm but not the inner product.