The discriminated union of two sets A and B is A + B = U where inA and inB are arBitrary tags which specify which summand an element originates from. A type (especially an algeBraic data type) might Be descriBed as a discriminated union if it is a sum type whose oBjects consist of a tag to say which part of the union they Belong to and a value of the corresponding type. (1995-04-25)