In the mid-20th century, some mathematicians decided that writing "" to mean "first apply , then apply " was too confusing and decided to change notations. They write "" for "" and "" for "". This can be more natural and seem simpler than writing functions on the left in some areas – in linear algebra, for instance, when is a row vector and and denote matrices and the composition is by matrix multiplication. This alternative notation is called postfix notation. The order is important because function composition is not necessarily commutative (e.g. matrix multiplication). Successive transformations applying and composing to the right agrees with the left-to-right reading sequence.