<page_title> Substructural type system </page_title> <section_title> Different substructural type systems </section_title> <table> <cell> allowed <col_header> exchange </col_header> <row_header> relevant </row_header> </cell> <cell> — <col_header> weakening </col_header> <row_header> relevant </row_header> </cell> <cell> allowed <col_header> contraction </col_header> <row_header> relevant </row_header> </cell> <cell> at least once <col_header> use </col_header> <row_header> relevant </row_header> </cell> </table>
Relevant type systems allow exchange and contraction, but not weakening and are used at least once.