isa?

(isa? child parent) (isa? h child parent) (isa? vec1 vec2)

Answers whether child relates to parent: equality, element-wise vector derivation (each component isa? the matching one), or ancestor membership through the hierarchy -- the global one, or h in the three-argument form. Answers true or false; the multimethod dispatch search is built on it.

A class spelling as child or parent is the keyword class answers for its values, as in a defmethod: String is :string, a record its tag, a throwable or stream class its name. A throwable or stream class keyword isa? each of its Java supers, interfaces included, and whatever they derive from, like the oracle's Java inheritance; every class isa? Object. On the interpreter and the JVM, class of a host object answers its class object, which isa? each class it extends or implements, and whatever they derive from, under any spelling of them: (isa? (class (java.util.ArrayList.)) java.util.List) is true.