The introduction should state clearly the object of the work, its scope and the main advances reported, with brief references to relevant results of other workers. In long papers it is helpful to indicate the way in which the paper is arranged and the results are presented.
Good introductions are particularly important in long reviews.
Subsections should be numbered 2.1, 2.2, 3.1, 3.2, etc. Where subsubsections are used they should be numbered 2.3.1, 2.3.2, etc. Mathematics should be clearly legible. Particular care should be taken with the position of subscripts and indices. Detailed instructions on the presentation of mathematics are available.