/= function compares numbers according to "equal" predicate. Result is true if no two numbers are equal to each other, otherwise result is false. Note that only two argument version result is negation of = function, that is (/= a b) is same as (not (= a b)).

(/= 1 2) => T
(/= 2 1) => T
(/= 2 2.001) => T
(/= 2 2) => NIL
(/= 2 2.0) => NIL
(/= 0.0 -0.0) => NIL
(/= #c(1.2 4.5) #c(1.2 4.5)) => NIL

(/= 1 2 3 4 5) => T
(/= 4 4 4 3 4) => NIL
(/= 1 2 3 4 4) => NIL
(/= 1 2 3 4.0 4) => NIL
(/= 5) => T