anchor.diff:  
   For trace of matrix we have stem:[\operatorname{tr}(AB)=\operatorname{tr}(BA)], stem:[\operatorname{tr}(-A)=-\operatorname{tr}(A)].
   
  -Finally for our block matrices stem:[M=\left[ \begin{array}{} A & B \\ C & D \\ \end{array} \right]], the determinant is
  +Finally for our block matrices stem:[M={\left[ \begin{array}{} A & B \\ C & D \\ \end{array} \right]}], the determinant is
   
   [stem]
   ++++
  
positive.code: W=(D-CA^{-1}B)^{-1}=\frac{1}{\left|M\right|}(\left|A\right|D-C(A^{\#}B))^{\#}
  ++++
  
  === Appendix
negative.code: 
  I only listed properties needed for derivation. If you are not familiar with these concepts, or want to know more about them, take a look at the wiki pages above.
  
  Let stem:[M^{-1}={\left[ \begin{array}{} A & B \\ C & D \\ \end{array} \right]}^{-1}={\left[ \begin{array}{} X & Y \\ Z & W \\ \end{array} \right]}].Let’s start with the top left corner.
  
  [stem]
  ++++
  