Clojure Syntax – Why Nested Shorthand Functions Can’t Be Written

the & in (defn full-name [& {first :first last :last}] indicates that all the remaining arguments should be gathered into a single collection. the map destructuring form following the & then takes the map created by the & apart again.

(defn full-name [& {first :first last :last}]...)
(full-name :first "Tom" :last "Brennan")

without the & becomes

 (defn full-name [{first :first last :last}]...)
(full-name {:first "Tom" :last "Brennan"})

for your other question: symbols and keywords implement the function interface so they can be called just like any other Clojure function. when called as a function they look themselves up in their argument which they expect to be a map (or something implementing the appropriate interface)

Unless you're using multiple else statements, you can just chain the conditions together with an "and". In Clojure, "and" is a macro which turns its arguments into a sequence of nested if statements.