Another more archaic option dispenses with the hyphen question altogether and employs the umlaut convention common in Germanic languages where a vowel following another vowel influences the pronunciation of the second vowel. Thus the words above become coöperation, coöperative, coöp, and coöper. However, this is convention is generally not used today.
In all cases, assume that in a dispute between american and english, the american use is wrong. ;-)))) keep to the Fen Causeway
