  We demonstrate a natural bijection between a subclass of alternating sign
matrices (ASMs) defined by a condition on the corresponding monotone triangle
which we call the gapless condition and a subclass of totally symmetric
self-complementary plane partitions defined by a similar condition on the
corresponding fundamental domains or Magog triangles. We prove that, when
restricted to permutations, this class of ASMs reduces to 312-avoiding
permutations. This leads us to generalize pattern avoidance on permutations to
a family of words associated to ASMs, which we call Gog words. We translate the
gapless condition on monotone trangles into a pattern avoidance-like condition
on Gog words associated. We estimate the number of gapless monotone triangles
using a bijection with p-branchings.
