Given Key is an argument type for function objects of type H, in
Table 36h is a value of type (possibly const) H,
u is an lvalue of type Key, and k is a value of a type convertible to
(possibly const) Key.

Thus all evaluations of the expression h(k) with the
same value for k yield the same result for a given execution of the program.

â€” end note]

For two different
values t1 and t2, the probability that h(t1) and h(t2)
compare equal should be very small, approaching 1.0/ numeric_limits<size_t>::max().