Sec. 7, 11.5, due March 26

From this section the only proof that confused me was the one for corollary 11.15.  They are using induction.  It says Now let a1,a2,...,ak+1 be k+1 integers, where p|a1,a2,...ak+1.  It seems as if they skipped a step here.  It seems as if they assume the statement is true for k+1 rather than k.