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A cube $ABCDEFGH$ with an edge length of $2$ units is placed in a coordinate system (see the picture). Let $S$ be the midpoint of the face $ABFE$, and let $K$ and $L$ be the midpoints of edges $DH$ and $CG$ consecutively. Find the standard equation of a plane $\alpha$ passing through the points $A$, $B$ and $L$, and calculate the distance of the point $S$ from $\alpha$.