\multicolumn
............
`\multicolumn{cols}{pos}{text}'
The `\multicolumn' is used to make an entry that spans several
columns. The first mandatory argument, `cols', specifies the number of
columns to span. The second mandatory argument, `pos', specifies the
formatting of the entry; `c' for centred, `l' for flushleft, `r' for
flushright. The third mandatory argument, `text', specifies what text
is to make up the entry.