Alice was sure within the first hour of meeting Bob that their families had software-entangled them since birth. It went beyond crude genetic matching: coordinate two people's most intimate software for their first twenty years of life and they will grow with statistically indistinguishable souls. Her eighteenth birthday's gift had been to know there was somebody almost-perfect for her and on her twenty-first's they would have had their first date.
It could still happen; Bob had been too distracted to notice her. That was a point against the system's promise, but a minor one. You couldn't be Alice and look at Bob without knowing who they had been for each other, how their experiences and choices had flowed between them without any other causal mechanism than the world's computational hum, which complemented and superseded laws physical and otherwise.
No. Alice was for Bob and Bob was for Alice. One persona-personality profile in two bodies. It wasn't chance that they were in the same party, had so many of the same interests, or felt deep and axiomatic desire for the same girl.
Her name was Trudy and Bob had only been dating her for a few months. Yet he would kill for her without a second thought. Alice knew this for a mathematical fact.
She left the party as discreetly as she could. Back at her apartment she picked up a pen and a piece of paper she could later burn and began to list the blind spots that somebody could use to kill her.