Thanks to both
yes, my question was this one: When the gm calls for a HARD task, it just means the investigator has to roll under the 50% of his skill, it doesnt reduce the skill to half of its original value.
So the result of a HARD task roll, it will always be a HARD success (or extreme, or critical).
and the result of an EXTREME task roll, will always be an EXTREME success (or critical), nothing less.
thanks
tommaso