This is a synonym for attribute cardinality constraint.
A constraint on the number of times that a specific attribute may be included in the same concept definition or expression.
Constraints on attribute cardinality apply only to non-redundant attributes. A redundant attribute is an attribute with a value that is subsumed by another attribute in the same concept definition or expression.
Cardinality constraints are represented by square brackets containing a minimum value value represented as an integer, optionally followed by two dots and a maximum value represented as an integer or as an asterisk *****.
If the maximum is omitted then the maximum cardinality is the same as the minimum cardinality.
If the maximum is an asterisk ***** the maximum cardinality is unlimited.
The following expression constraint is satisfied by any clinical finding whose definition has two or more non-redundant finding sites, irrespective of the attribute group in which they are contained.
< : [2..*] = <