A series of lines marked up by \[...\\...\] may be divided into
2 or 3 left-aligned columns by inserting & characters in each
line. The result is as if one had used an explicit tabular or
array environment (according to the current mode) with the
argument @{}l@{}l@{}l@{}. Note that no space at all is
inserted between the columns. In text mode, one may use e.g.
~&~ to get space between columns; in math mode, the correct
spacing around binary operations and relations can be obtained by
inserting {} for arguments that have been separated by
&s.