 A subgroup of formula_19 is said to be "derived from a quaternion algebra" if it can be obtained through the following construction.Let formula_2 be a number field which has exactly two embeddings into formula_21 whose image is not contained in formula_22 (one conjugate to the other).Let formula_23 be a quaternion algebra over formula_2 such that for any embedding formula_25 the algebra formula_26 is isomorphic to the Hamilton quaternions.