# Confusion about left/right-handed spinor notations

Peskin & Schroeder eq (3.78) states that

$$(\bar{u}_{1R}\sigma^\mu u_{2R})(\bar{u}_{3R}\sigma_\mu u_{4R})=\cdots$$

But I don't understand what the $$u_{1R}$$ means. Since 4-component Dirac spinor consists of left-handed and right-handed 2-component spinors, we can say

$$\psi(x)=\begin{pmatrix}u_1(p)\\u_2(p)\\u_3(p)\\u_4(p) \end{pmatrix}e^{-ipx}=\begin{pmatrix}\psi_L\\ \psi_R\end{pmatrix}$$ for the positive frequency solutions. That is, $$u_1,u_2$$ correspond to the left-handed part and $$u_3,u_4$$ correspond to the right-handed part. But then, the above notations like $$u_{1R},u_{2R}$$ do not make any sense to me.

It is stated above the quoted formula: "By sandwiching identity (3.77) between the right-handed portions (i.e., lower half) of Dirac spinors $$u_1$$, $$u_2$$, $$u_3$$, $$u_4$$, we find the identity" (3.78).
Thus $$u_{1R}$$ simply means the right-handed component of the spinor $$u_1$$; the "$$1$$" does not indicate a component here. Analogously for the other spinors.