[Xy-pic] Colour only a pice of curve

[Diego]

Hi,
in reference to the following piece of code, I'm trying to paint the curve
from 0 to 1 in a different colour but only between the intersection points
"i1" and "i2".

%----
\begin{xy}
(0,0)*{0}="o";<5mm,0mm>:<0mm,5mm>::,
(5,8)*{1}="b", (-5,0)="c", (5,0)="d",

(-1.5,2.5)="c1", (1.5,2.5)="c2",
"c";"d" **\crv{"c1"&"c2"},

(-4,10)="d1", (4,10)="d2",
"c";"d" **\crv{"d1"&"d2"},

(0,5)="q1", (2,9)="q2",
"o";"b" **\crv{"q1"&"q2"}
?!{"c";"d" **\crv{~**{}"c1"&"c2"}}*@{>}="i1"
?!{"c";"d" **\crv{~**{}"d1"&"d2"}}*@{<}="i2",
\end{xy}
%----
[image: Immagine incorporata 2]
At the moment my workaround is to crate three \crv:
- from 0 to "i1";
- from "i1" to "i2" using the syntax "i1";"i2" **[colour]\crv{..&..};
- from "i2" to 1.

With a software like Geogebra I can find the rights coordinates of the
control points so that the result seems to be only one Bezier curve, but
it's a lot of work.

Is there a more simple way to achieve the same result?

Thanks

-- 
Diego
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