Arrows are provided to supplement \xleftarrow and \xrightarrow of teh AMSMath package: \xlongequal \xLongleftarrow \xLongrightarrow \xLongleftrightarrow \xLeftrightarrow \xlongleftrightarrow \xleftrightarrow \xlongleftarrow \xlongrightarrow The author is Chim Cut Canh.