All contacts and vias between layers are specified in the contact section. Each line in this section defines the connectivity of one type of contact. The line begins with the name of the contact layer followed by two lists of comma separated layer names. Each list contains the layer types on a given ``side'' of the contact. Make sure that each list does not contain any white space as the white space is used to delimit the end of one list and the beginning of the other. The layer names must have been specified previously in the types section.