universe of discourse = all inner planets of our solar system, Earth, Mars,
a: Mercury, b: Venus, c: Earth, d: Mars,
- Sx: "x has a natural satellite (a moon)."
- I.e., 'Sc' and 'Sd' are true as 'S' is associated only
with the planets having moons: Earth (c) and Mars (d).
- Tx: "x is a terrestrial (rocky) planet".
- I.e. 'Sa','Sb','Sc', and 'Sd' are all true because
the inner planets (unlike the outer ones) are terrestrial as opposed
to gassy or icy.
- Ixy: "x orbits inside y".
- So, for examples, 'Iab' is true: Mercury orbits inside
Venus. So are: 'Iac',Iad','Ibc','Ibd',and 'Icd'.