> Euclidean geometers however only recognise angles between straight lines.
Geometers in general only recognize angles between straight line - the angle between curves is typically defined as the angles between their tangent lines. Understood this way, the example of a diameter cutting a circle is *not* a counterexample to the postulate in question.
> Euclidean geometers however only recognise angles between straight lines.
Geometers in general only recognize angles between straight line - the angle between curves is typically defined as the angles between their tangent lines. Understood this way, the example of a diameter cutting a circle is *not* a counterexample to the postulate in question.