i := zone.overlays(z)

Get the number of overlays available in the zone. This number will normally be 2.

A value of 1 can occur if the zone is deformed sufficiently to cause one overlay to contain a tetra with zero or negative volume, or if the zone was deliberately created with one overlay during the zone cmodel assign command.

A value of 0 means the zone has never had a constitutive model assigned, and therefore internal tetra have never been created.

Returns:i - the number of overlays: 2, 1, or 0
Arguments:z - a pointer to a zone