“…Since every countable tree is a minor of the half‐grid, Theorem 1.5 implies that all countable trees are
‐ubiquitous, see Corollary 9.4. We remark that while it has been shown that all trees are ubiquitous with respect to the topological minor relation [
4], the question of whether all uncountable trees are
‐ubiquitous has remained open, and we hope to resolve this in a paper in preparation.…”