Suppose the Bloch function uk(x)exp(ikx) is a solution of the Schrödinger equation for a one-dimensional crystal with repeat length (i.e. unit cell size) a in the x direction, with eigenenergy Ek. Then there is a function uk+ uk + 2 pi/a (x) also periodic with repeat length a, such that ik+2 pi/a (x)exp[i(k+2 pi/a)x] is also a solution of the same Schrödinger equation with the same eigenenergy Ek. True/False?