graph {
A1 [label="A's PDP-11"]
AM [label="A's master key"]
A2 [label="A's Osborne 2"]
B1 [label="B's Dynabook"]
BM [label="B's master key"]
B2 [label="B's VAX"]
A1 -- AM
AM -- A2
AM -- BM
B1 -- BM
BM -- B2
}