The husk and stray are counted as sub-variants of existing mobs as opposed to entirely new mobs, hence why you are unable to simply type /summon Stray or /summon Husk. There was supposed to be spawn eggs for them, but it seems they were removed either intentionally or by accident in the final release.
Axiomatic method, in logic, a procedure by which an entire system (e.g., a science) is generated in accordance with specified rules by logical deduction from certain basic propositions (axioms or postulates), which in turn are constructed from a few terms taken as primitive.
axiom An axiom is a statement that everyone believes is true, such as supply equals demand or the only constant is change. Mathematicians use axiom to refer to established proofs. Many axioms are so widely used they become clichÃ©sâhere's one to help you remember what the word means.