# [Xy-pic] half-solid ellipse

Aaron Lauda A.Lauda at dpmms.cam.ac.uk
Mon Mar 28 20:36:45 CEST 2005

```Try this:

\[ \xy
(7,0)*\ellipse(1,3){.}; (7,0)*\ellipse(1,3)_,=:a(180){-};
(0,2.5)*\ellipse(1,3){-}; (0,-2.5)*\ellipse(1,3){-};
(14,3)*{}="TR"; (14,-3)*{}="BR"; (0,8)*{}="TTL"; (0,2)*{}="TBL";
(0,-2)*{}="BTL"; (0,-8)*{}="BBL"; (10,3)*{}="A"; (10,-3)*{}="B";
"TTL";"A" **\crv{(5,8) & (3,4)}; "A";"TR" **\dir{-}; "BBL";"B"
**\crv{(5,-8) & (3,-4)}; "B";"BR" **\dir{-}; "TBL";"BTL"
**\crv{(3,2) & (3,-2)};
\endxy \]

Best,
Aaron

On Sun, 27 Mar 2005, Chris Brav wrote:

> hi. i'm trying to make 2D cobordism diagrams. i like to draw them from
> left to right, with solid circles on the in direction (left-hand) and half-solid,
> half-dotted circles on the out direction (right-hand), with the solid half
> "out front" and the dotted half "behind". a. lauda's code does this for diagrams drawn
> from top to bottom, but i can't get it to work from left to right.
>
> here is my code:
>
> \[ \xy
> (7,0)*\ellipse(1,3){.};
> (7,0)*\ellipse(1,3)__,=:a(270){-};
> (0,2.5)*\ellipse(1,3){-};
> (0,-2.5)*\ellipse(1,3){-};
> (14,3)*{}="TR";
> (14,-3)*{}="BR";
> (0,8)*{}="TTL";
> (0,2)*{}="TBL";
> (0,-2)*{}="BTL";
> (0,-8)*{}="BBL";
> (10,3)*{}="A";
> (10,-3)*{}="B";
> "TTL";"A" **\crv{(5,8) & (3,4)};
> "A";"TR" **\dir{-};
> "BBL";"B" **\crv{(5,-8) & (3,-4)};
> "B";"BR" **\dir{-};
> "TBL";"BTL" **\crv{(3,2) & (3,-2)};
> \endxy \]
>
> the trouble is line #3. i presume =:a() is supposed to set an angle, but
> no matter what angle i try, i can't get rid of the extra solid part
> showing from "behind".
>
> any suggestions?
>
> chris brav
>
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>

```