\form#0:$A=\frac{df}{dx}|_{x0,u0}$
\form#1:$A=\frac{d}{dx}f(x,u)|_{x0,u0}$
\form#2:$A=\frac{d}{du}f(x,u)|_{x0,u0}$
\form#3:$x \sim epdf(rv)$
\form#4:\[ f(x|a,b) = \prod f(x_i|a_i,b_i) \]