 Convention (association to the left): When more than two terms \(M_1 M_2 M_3 \ldots M_n\) are juxtaposed we can recover the missing parentheses by associating to the left: reading from left to right, group \(M_1\) and \(M_2\) together, yielding \((M_1 M_2)M_3 \ldots M_n\); then group \((M_1 M_2)\) with \(M_3\): \(((M_1 M_2)M_3)\ldots M_n\), and so forth.