Although Conway's Game of Life is usually defined on an infinite grid, some implementations exist that use a finite grid. Primitive implementations have a 'border', where strange effects occur. For example, half of a pulsar or other inductor can form on the boundary of the grid. To circumvent this, some sort of wraparound is needed. This category contains different topologies, or ways in which the boundaries can be 'stitched together' to form a contiguous surface.