Knot signature functions are independent

To each unit complex number with positive imaginary part there is defined a Tristram-Levine knot signature function. The set of all such signature functions is linearly independent as a set of functions defined on the set of all knots. The set of averaged signature functions forms a linearly independent set of homomorophisms on the knot concordance group. However, for each unit root of an Alexander polynomial, there is a slice knot with nonvanishing signature at that root and its conjugate, and nowhere else. These results hold for knots in all odd dimension.