The Kullback–Leibler divergence from N 0 ( μ 0 , Σ 0 ) {\displaystyle {\mathcal {N}}_{0}({\boldsymbol {\mu }}_{0},{\boldsymbol {\Sigma }}_{0})} to N 1 ( μ 1 , Σ 1 ) {\displaystyle {\mathcal {N}}_{1}({\boldsymbol {\mu }}_{1},{\boldsymbol {\Sigma }}_{1})} , for non-singular matrices Σ 0 and Σ 1 , is: [8]

* External irritants can sometimes cause a previously
retractable prepuce to become non-retractable due to swelling
of the tissues. If a child whose prepuce was retractable
becomes non-retractable, environmental factors should be
investigated. One known culprit is bubble bath. If a child is
taking bubble baths and the prepuce becomes non-retractable,
the bubble bath should be discontinued. See Penile Hygiene in the Intact
Non-circumcised Male for comprehensive information on
foreskin care.*