“…In particular, for a rank 3 permutation group G on P, if S := (P, L) is a linear space with at least three points on every line such that G Aut(S) and G has exactly two orbits L 1 and L 2 on L, then (P, L 1 ) and (P, L 2 ) are proper partial linear spaces that admit G and have disjoint collinearity relations; in fact, the converse of this statement also holds (see Lemma 2.11). Observe that S is a 2-(v, k, 1) design -that is, a linear space with v points and line-size k -precisely when (P, L 1 ) and (P, L 2 ) both have line-size k. Those 2-(v, k, 1) designs admitting a rank 3 automorphism group G with two orbits on lines have been studied in the special case of affine planes (for example, [3]) and in general when G is an affine primitive group [4,46]. For each partial linear space S in Table 1, we state whether S can be obtained from a 2-(v, k, 1) design using a rank 3 group as above; when this design is an affine plane (that is, when v = k 2 ), we state this instead, and when this affine plane is well known, we give its name.…”