(#K{a0,a1...} === #K{b0,b1...}) (same tag)
--------------------------------------- EQL-CTR-MAT
For SUC (1n+): ↑(pred === pred)
For CON (<>): ↑((head === head) & ↑(tail === tail))
Others: (a0 === b0) & (a1 === b1) & ...
(#K{...} === #L{...}) (different tag)
------------------------------------- EQL-CTR-MIS
#0