The preposition onto written as one word （instead of on to） is recorded from the early 18th century and has been widely used ever since, but is still not wholly accepted as part of standard British English （unlike into, for example）. Many style guides still advise writing it as two words, and that is the practice followed in this dictionary. However, onto is more or less the standard form in US English and in the specialized mathematics sense. Nevertheless, it is important to maintain a distinction between the preposition onto or on to and the use of the adverb on followed by the preposition to： she climbed on to （or onto） the roof but let's go on to （not onto） the next point.