@MISC{TREES_1.MIZ,
  AUTHOR = {Bancerek, Grzegorz},
  TITLE = {Introduction to Trees},
  DAY = {25},
  MONTH = {October},
  YEAR = {1989},
  ADDRESS1 = {Warsaw University\\Bia{\l}ystok},
  SUMMARY = {The article consists of two parts: the first one deals with the concept of
the prefixes of a finite sequence, the second one introduces and deals with
the concept of tree. Besides some auxiliary propositions concerning
finite sequences are presented. The trees are introduced as non-empty sets
of finite sequences of natural numbers which are closed on prefixes and
on sequences of less numbers (i.e. if $\langle n_1$, $n_2$, $\dots$,
 $n_k\rangle$ is a vertex (element) of a tree and $m_i \leq n_i$
for $i = 1$, $2$, $\dots$, $k$, then $\langle m_1$, $m_2$, $\dots$,
 $m_k\rangle$ also is). Finite trees, elementary trees with $n$ leaves,
the leaves and the subtrees of a tree, the inserting of a tree into another
tree, with a node used for determining the place of insertion,
antichains of prefixes, and height and width of finite trees
are introduced.}}

