= Composition rule for chordal Loewner driving functions
{title2=$\widehat U_s=U_{t+s}-U_t$}
After time $t$, map remaining domains by $g_t-U_t$. The new <mapping-out function> at elapsed time $s$ is $\widehat g_s(z)=g_{t+s}(g_t^{-1}(z+U_t))-U_t$. Direct differentiation of the <Chordal Loewner equation> proves that its driver is $U_{t+s}-U_t$, and its <half-plane capacity> is $2s$. Defining transformed hulls as complements of transformed domains avoids ambiguity at the old hull boundary.
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