71. The combination of claim 70 wherein said input signals are essentially periodic and wherein said preselected portions lie in the range from 1/4 to 3/4 of the period.
71. The combination of claim 70 wherein said input signals are essentially periodic and wherein said preselected portions lie in the range from 1/4 to 3/4 of the period. 72. The combination of claim 71 wherein said predetermined portion is substantially 1/2.