Given a PRF E:K$\backslash$times $\{0,1\}^$n$->\{0,1\}^$m$,$ we construct F:K$\backslash$times $\{0,1\}^($n$-1)->\{0,1\}^2$m as follows:

F$($K$,$x$)$:$=$E$($K$,$x$||0)||$E$($K$,$x$||1).$

Is F$($K$,)$ still a PRF$?$ If yes, give a brief proof, if not, give a brief attack showing the violation of PRF definition.