Grebes are not mammals.
The only types of mammals that lay eggs are platypuses and echidnas. Platypuses are not hyrax. Echidnas are not hyrax. No mammals are invertebrates. All animals are either vertebrates or invertebrates. Mammals are animals. Hyraxes are mammals. Grebes lay eggs. Grebes are not platypuses and also not echidnas.
∀x ((Mammal(x) ∧ LayEgg(x)) → (Platypuses(x) ⊕ Echidnas(x))) ∀x (Platypuses(x) → ¬Hyrax(x)) ∀x (Echidnas(x) → ¬Hyrax(x)) ∀x (Mammal(x) → ¬Invertebrate(x)) ∀x (Animal(x) → Invertebrate(x) ⊕ Vertebrate(x)) ∀x (Mammal(x) → Animal(x)) ∀x (Hyrax(x) → Mammal(x)) ∀x (Grebes(x) → LayEgg(x)) ∀x (Grebes(x) → (¬Platypuses(x) ∧ ¬Echidnas(x)))