This is really the same as "Interrupt after 1/2". It takes two
calls, as in "Sandwich Swing Thru around Mix". Do the first half
of the first call, do the second call, and do the last half of the first call.
The first call does not need to have an even number of parts — it just
needs to be able to be interrupted at the halfway point.
\syhlines{b4n,g4n,b1n,g1n}
\sxhlines{b2s,g2s,b3s,g3s}
before Sandwich Wheel Around around Ferris Wheel
after
Applications of Sandwich have 3 parts, independently of the structure
of the calls. Of course, nested concepts can go more deeply into the
structure of the calls.
\syhlines{b2n,g2s,g3n,b3s}
\syhlines{g1s,b4s,b1s,g4s}
before Finally 1/2, Sandwich Contour the Line around Explode the Wave