+These comparison operators are "polymorphic". This is a notion we'll discuss later when we get to types, but in the present context it means that you can apply `==` to two numbers, or to two booleans, and so on. In Kapulet, OCaml, and Haskell, however, you cannot apply that comparison to a number and a boolean at the same time. That will fail as a type error, instead of evaluating to `'false`.
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+Also, these languages (and Scheme too) behave in idiosyncratic ways if you try to compare two function values for equality. The equivalence of function values is not in general recursively decidable; it may be possible in some specific cases to give you a definite yes-or-no answer, but you'll have to look up the specific rules for (each implementation of) each language. I recommend that you in general just avoid comparing function values for equality.
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+Scheme has a whole bunch of equality functions. First, there are functions restricted to specific kinds of values: `=` for numbers, `symbol=?` for symbolic atoms, `boolean=?` for booleans (this is more familiar to us as "iff"), and so on. Those functions fail if called with arguments that aren't of the expected types. Scheme also has a couple of unrestricted equality functions, which can take arguments of any type, and the arguments need not even be of the same type (but if they're not, they'll always be counted as unequal). The two most fundamental of these are `eqv?` and `equal?`. They behave the same for numbers (at least, for "exact" numbers like integers), for symbols, for booleans, and the like. As we'll discuss [[below|rosetta1#mlists]], containers in Scheme (lists, pairs, vectors, strings) are generally "mutable", so there's a choice when comparing two such containers whether we're asking if the containers merely *happen now to contain corresponding values* (including, if their elements are themselves containers, they too containing corresponding values). Or whether we're asking if the containers *occupy the same mutable location in memory*, so that it'd be impossible for them to become unequal at any stage in the program's evaluation. The first comparison is expressed by `equal?`; the second by `eqv?`. (You may also see Scheme programs that use the predicate `eq?`. This is a variant of `eqv?` that may sometimes be more efficient.)