A pseudo-Daugavet property for narrow projections in Lorentz spaces

Let $X$ be a rearrangement-invariant space. An operator $T:X\to X$ is called narrow if for each measurable set $A$ and each $ϵ>0$ there exists $x \in X$with$x^2= \chi_A, \int x d \mu = 0$and$| Tx | < \epsilon$. In particular all compact operators are narrow. We prove that if $X$ is a Lorentz function space $L_{w,p}$ on [0,1] with $p>2$, then there exists a constant $k_X>1$ so that for every narrow projection $P$ on $L_{w,p}$ $| Id - P | \geq k_X. $Thisgeneralizesearlierresultson$L_p$ and partially answers a question of E. M. Semenov. Moreover we prove that every rearrangement-invariant function space $X$ with an absolutely continuous norm contains a complemented subspace isomorphic to $X$ which is the range of a narrow projection and a non-narrow projection, which gives a negative answer to a question of A.Plichko and M.Popov.