Lyases are enzymes that cleave C-C, C-O, C-N and other bonds by means other than by hydrolysis or oxidation. They differ from other enzymes in that two (or more) substrates are involved in one reaction direction, but there is one compound fewer in the other direction. When acting on the single substrate, a molecule is eliminated and this generates either a new double bond or a new ring. The systematic name is formed according to 'substrate group-lyase'. In common names, expressions like decarboxylase, aldolase, etc. are used. 'Dehydratase' is used for those enzymes that eliminate water. In cases where the reverse reaction is the more important, or the only one to be demonstrated, 'synthase' may be used in the name.