\sqsubseteq

from The Free On-line Dictionary of Computing (8 July 2008)

\sqsubseteq

   {LaTeX} name for a symbol like a capital E without the bottom
   half of its vertical line.

   In {domain theory},

   	x \sqsubseteq y

   means x is no more defined that y.  This expression only has
   meaning if x and y are {comparable} elements of some
   {partially ordered set}.

   (1994-11-24)