We consider arrangements of n pseudo-lines in the Euclidean plane where each pseudo-line $$\ell _i$$
ℓ
i
is represented by a bi-infinite connected x-monotone curve $$f_i(x)$$
f
i
(
x
)
, $$x \in \mathbb {R}$$
x
∈
R
, such that for any two pseudo-lines $$\ell _i$$
ℓ
i
and $$\ell _j$$
ℓ
j
with $$i \!<\! j$$
i
<
j
, the function $$x \!\mapsto \! f_j(x) \!-\! f_i(x)$$
x
↦
f
j
(
x
)
-
f
i
(
x
)
is monotonically decreasing and surjective (i.e., the pseudo-lines approach each other until they cross, and then move away from each other). We show that such arrangements of approaching pseudo-lines, under some aspects, behave similar to arrangements of lines, while for other aspects, they share the freedom of general pseudo-line arrangements. For the former, we prove:
There are arrangements of pseudo-lines that are not realizable with approaching pseudo-lines.
Every arrangement of approaching pseudo-lines has a dual generalized configuration of points with an underlying arrangement of approaching pseudo-lines.
For the latter, we show:
There are $$2^{\Theta (n^2)}$$
2
Θ
(
n
2
)
isomorphism classes of arrangements of approaching pseudo-lines (while there are only $$2^{\Theta (n \log n)}$$
2
Θ
(
n
log
n
)
isomorphism classes of line arrangements).
It can be decided in polynomial time whether an allowable sequence is realizable by an arrangement of approaching pseudo-lines.
Furthermore, arrangements of approaching pseudo-lines can be transformed into each other by flipping triangular cells, i.e., they have a connected flip graph, and every bichromatic arrangement of this type contains a bichromatic triangular cell.