The late-’70s post-/art-/avant-punk cake is not wholly eaten. There’s a piece left for everyone at the table, and apparently these days it’s up to labels like Kill Rock Stars, Soul Jazz and Acute to serve the platters. Enter Essential Logic. Back in the old X-Ray Spex days (1977), Logic’s eardrum-shattering sax outbursts were the meaty substance to Poly Styrene’s evocative, stripped-to-the-bone sass-funk. But the friendship lasted for only one summer. Abandoned by her bandmates, Logic founded her own band, Essential Logic, in 1978. EL triggered all the stimuli of the English post-punk scene: listen to “Wake Up,” which walks the thin line between dangerous intensity and explosive disco-ness. Over the years, Logic worked with such divergent bands as The Raincoats, Swell Maps, Scritti Politti and Red Krayola. Some of the contributions to this astonishing double-CD aren’t really necessary. But even the Tori Amos-like later stuff does refine this detached beauty, which elevated Essential Logic above many of their contemporaries.