2 added 2 characters in body

Mikhail,

Here's an upper cap in xy-pic

\xymatrix{ X'\ar[rd]^{[1]}\ar[dd]^{[1]} & & Z\ar[ll] \\ & Y\ar[ru]\ar[ld] & \\ Z'\ar[rr]^{[1]} & & X\ar[lu]\ar[uu] }

at least it's enough of one to get you started. Note that I didn't construct it by hand. I have a script for building these kinds of diagrams visually:

http://www.math.purdue.edu/~dvb/scripts/arraymaker

If it's useful to you, help yourself.

1

Mikhail,

Here's an upper cap in xy-pic

\xymatrix{ X'\ar[rd]^{[1]}\ar[dd]^{[1]} & & Z\ar[ll] \ & Y\ar[ru]\ar[ld] & \ Z'\ar[rr]^{[1]} & & X\ar[lu]\ar[uu] }

at least it's enough of one to get you started. Note that I didn't construct it by hand. I have a script for building these kinds of diagrams visually:

http://www.math.purdue.edu/~dvb/scripts/arraymaker

If it's useful to you, help yourself.