In this paper we present an implicit dictionary with the working set property i.e. a dictionary supporting \op{insert}($e$), \op{delete}($x$) and \op{predecessor}($x$) in~$\O(\log n)$ time and \op{search}($x$) in $\O(\log\ell)$ time, where $n$ is the number of elements stored in the dictionary and $\ell$ is the number of distinct elements searched for since the element with key~$x$ was last searched for. The dictionary stores the elements in an array of size~$n$ using \emph{no} additional space. In the cache-oblivious model the operations \op{insert}($e$), \op{delete}($x$) and \op{predecessor}($x$) cause $\O(\log_B n)$ cache-misses and \op{search}($x$) causes $\O(\log_B \ell)$ cache-misses.