thus A1: 3 ! = (2 + 1) !
.= 2 * 3 by NEWTON:14, NEWTON:15
.= 6 ; :: thesis: 4 ! = 24
thus 4 ! = (3 + 1) !
.= 6 * 4 by A1, NEWTON:15
.= 24 ; :: thesis: verum