text: * Orbifold signature: 
  * Coxeter notation (rectangular): [&infin;,2,&infin;] or [&infin;]×[&infin;]
  * Coxeter notation (square): [4,1,4] or [1,4,4,1]
  * Lattice: rectangular
  * Point group: D
  * The group pmm has reflections in two perpendicular directions, and four rotation centres of order two (180°) located at the intersections of the reflection axes.
  ;Examples of group pmm