A ^ ^ is either a creation operator or an annihilation operator. If A ^ ^ is a creation operator, all above products, such as A ^ ^ : B ^ ^ C ^ ^ D ^ ^ E ^ ^ F ^ ^ … … : , are already normal ordered and require no further manipulation. Because A ^ ^ is to the left of all annihilation operators in A ^ ^ B ^ ^ C ^ ^ D ^ ^ E ^ ^ F ^ ^ … … , any contraction involving it will be zero. Thus, we can add all contractions involving A ^ ^ to the sums without changing their value. Therefore, if A ^ ^ is a creation operator, Wick's theorem holds for A ^ ^ B ^ ^ C ^ ^ D ^ ^ E ^ ^ F ^ ^ … … .