  Assume that $A$, $B$ are Banach algebras and $m:A\times B\to B$,
$m^\prime:A\times A\to B$ are bounded bilinear mappings. We will study the
relation between Arens regularities of $m$, $m^\prime$ and the Banach algebras
$A$, $B$. For Banach $A-bimodule$ $B$, we show that $B$ factors with respect to
$A$ if and only if $B^{**}$ is an unital $A^{**}-module$, and we define locally
topological center for elements of $A^{**}$ and will show that when locally
topological center of mixed unit of $A^{**}$ is $B^{**}$, then $B^*$ factors on
both sides with respect to $A$ if and only if $B^{**}$ has a unit as
$A^{**}-module$.
