Four operations, and which sources demonstrate each

A filled square means that source explicitly treats that operation. Only Lance Martin sets out all four. Every other source demonstrates a subset, which is why no single account reads as the whole picture.

Compression is the only one of the four that destroys information. That is definitional, not a measurement: the other three move material, retrieve it or hold it apart, while this one discards it to make things fit.

Coverage assessed from each source's own text. Sources: Lance Martin (June 2025); Liu et al., arXiv:2307.03172; Packer et al., arXiv:2310.08560; Mei et al., arXiv:2507.13334; Yichao Ji, Manus (July 2025); Zhang et al., arXiv:2510.04618; Hangfei Lin, Google (December 2025); Anthropic (July 2026).